linux/ipc/sem.c
Davidlohr Bueso a5f4db8771 ipc/sem: make semctl setting sempid consistent
As indicated by bug#112271, Linux sets the sempid value upon semctl, and
not only for semop calls.  However, within semctl we only do this for
SETVAL, leaving SETALL without updating the field, and therefore rather
inconsistent behavior when compared to other Unices.

There is really no documentation regarding this and therefore users
should not make assumptions.  With this patch, along with updating
semctl.2 manpages, this scenario should become less ambiguous As such,
set sempid on SETALL cmd.

Also update some in-code documentation, specifying where the sempid is
set.

Passes ltp and custom testcase where a child (fork) does SETALL to the
set.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reported-by: Philip Semanchuk <linux_kernel.20.ick@spamgourmet.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Herton R. Krzesinski <herton@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-22 15:36:02 -07:00

2221 lines
56 KiB
C

/*
* linux/ipc/sem.c
* Copyright (C) 1992 Krishna Balasubramanian
* Copyright (C) 1995 Eric Schenk, Bruno Haible
*
* /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
*
* SMP-threaded, sysctl's added
* (c) 1999 Manfred Spraul <manfred@colorfullife.com>
* Enforced range limit on SEM_UNDO
* (c) 2001 Red Hat Inc
* Lockless wakeup
* (c) 2003 Manfred Spraul <manfred@colorfullife.com>
* Further wakeup optimizations, documentation
* (c) 2010 Manfred Spraul <manfred@colorfullife.com>
*
* support for audit of ipc object properties and permission changes
* Dustin Kirkland <dustin.kirkland@us.ibm.com>
*
* namespaces support
* OpenVZ, SWsoft Inc.
* Pavel Emelianov <xemul@openvz.org>
*
* Implementation notes: (May 2010)
* This file implements System V semaphores.
*
* User space visible behavior:
* - FIFO ordering for semop() operations (just FIFO, not starvation
* protection)
* - multiple semaphore operations that alter the same semaphore in
* one semop() are handled.
* - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and
* SETALL calls.
* - two Linux specific semctl() commands: SEM_STAT, SEM_INFO.
* - undo adjustments at process exit are limited to 0..SEMVMX.
* - namespace are supported.
* - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtine by writing
* to /proc/sys/kernel/sem.
* - statistics about the usage are reported in /proc/sysvipc/sem.
*
* Internals:
* - scalability:
* - all global variables are read-mostly.
* - semop() calls and semctl(RMID) are synchronized by RCU.
* - most operations do write operations (actually: spin_lock calls) to
* the per-semaphore array structure.
* Thus: Perfect SMP scaling between independent semaphore arrays.
* If multiple semaphores in one array are used, then cache line
* trashing on the semaphore array spinlock will limit the scaling.
* - semncnt and semzcnt are calculated on demand in count_semcnt()
* - the task that performs a successful semop() scans the list of all
* sleeping tasks and completes any pending operations that can be fulfilled.
* Semaphores are actively given to waiting tasks (necessary for FIFO).
* (see update_queue())
* - To improve the scalability, the actual wake-up calls are performed after
* dropping all locks. (see wake_up_sem_queue_prepare(),
* wake_up_sem_queue_do())
* - All work is done by the waker, the woken up task does not have to do
* anything - not even acquiring a lock or dropping a refcount.
* - A woken up task may not even touch the semaphore array anymore, it may
* have been destroyed already by a semctl(RMID).
* - The synchronizations between wake-ups due to a timeout/signal and a
* wake-up due to a completed semaphore operation is achieved by using an
* intermediate state (IN_WAKEUP).
* - UNDO values are stored in an array (one per process and per
* semaphore array, lazily allocated). For backwards compatibility, multiple
* modes for the UNDO variables are supported (per process, per thread)
* (see copy_semundo, CLONE_SYSVSEM)
* - There are two lists of the pending operations: a per-array list
* and per-semaphore list (stored in the array). This allows to achieve FIFO
* ordering without always scanning all pending operations.
* The worst-case behavior is nevertheless O(N^2) for N wakeups.
*/
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/time.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>
#include <linux/uaccess.h>
#include "util.h"
/* One semaphore structure for each semaphore in the system. */
struct sem {
int semval; /* current value */
/*
* PID of the process that last modified the semaphore. For
* Linux, specifically these are:
* - semop
* - semctl, via SETVAL and SETALL.
* - at task exit when performing undo adjustments (see exit_sem).
*/
int sempid;
spinlock_t lock; /* spinlock for fine-grained semtimedop */
struct list_head pending_alter; /* pending single-sop operations */
/* that alter the semaphore */
struct list_head pending_const; /* pending single-sop operations */
/* that do not alter the semaphore*/
time_t sem_otime; /* candidate for sem_otime */
} ____cacheline_aligned_in_smp;
/* One queue for each sleeping process in the system. */
struct sem_queue {
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
int pid; /* process id of requesting process */
int status; /* completion status of operation */
struct sembuf *sops; /* array of pending operations */
struct sembuf *blocking; /* the operation that blocked */
int nsops; /* number of operations */
int alter; /* does *sops alter the array? */
};
/* Each task has a list of undo requests. They are executed automatically
* when the process exits.
*/
struct sem_undo {
struct list_head list_proc; /* per-process list: *
* all undos from one process
* rcu protected */
struct rcu_head rcu; /* rcu struct for sem_undo */
struct sem_undo_list *ulp; /* back ptr to sem_undo_list */
struct list_head list_id; /* per semaphore array list:
* all undos for one array */
int semid; /* semaphore set identifier */
short *semadj; /* array of adjustments */
/* one per semaphore */
};
/* sem_undo_list controls shared access to the list of sem_undo structures
* that may be shared among all a CLONE_SYSVSEM task group.
*/
struct sem_undo_list {
atomic_t refcnt;
spinlock_t lock;
struct list_head list_proc;
};
#define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS])
#define sem_checkid(sma, semid) ipc_checkid(&sma->sem_perm, semid)
static int newary(struct ipc_namespace *, struct ipc_params *);
static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
#endif
#define SEMMSL_FAST 256 /* 512 bytes on stack */
#define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
/*
* Locking:
* sem_undo.id_next,
* sem_array.complex_count,
* sem_array.pending{_alter,_cont},
* sem_array.sem_undo: global sem_lock() for read/write
* sem_undo.proc_next: only "current" is allowed to read/write that field.
*
* sem_array.sem_base[i].pending_{const,alter}:
* global or semaphore sem_lock() for read/write
*/
#define sc_semmsl sem_ctls[0]
#define sc_semmns sem_ctls[1]
#define sc_semopm sem_ctls[2]
#define sc_semmni sem_ctls[3]
void sem_init_ns(struct ipc_namespace *ns)
{
ns->sc_semmsl = SEMMSL;
ns->sc_semmns = SEMMNS;
ns->sc_semopm = SEMOPM;
ns->sc_semmni = SEMMNI;
ns->used_sems = 0;
ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
}
#ifdef CONFIG_IPC_NS
void sem_exit_ns(struct ipc_namespace *ns)
{
free_ipcs(ns, &sem_ids(ns), freeary);
idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr);
}
#endif
void __init sem_init(void)
{
sem_init_ns(&init_ipc_ns);
ipc_init_proc_interface("sysvipc/sem",
" key semid perms nsems uid gid cuid cgid otime ctime\n",
IPC_SEM_IDS, sysvipc_sem_proc_show);
}
/**
* unmerge_queues - unmerge queues, if possible.
* @sma: semaphore array
*
* The function unmerges the wait queues if complex_count is 0.
* It must be called prior to dropping the global semaphore array lock.
*/
static void unmerge_queues(struct sem_array *sma)
{
struct sem_queue *q, *tq;
/* complex operations still around? */
if (sma->complex_count)
return;
/*
* We will switch back to simple mode.
* Move all pending operation back into the per-semaphore
* queues.
*/
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
struct sem *curr;
curr = &sma->sem_base[q->sops[0].sem_num];
list_add_tail(&q->list, &curr->pending_alter);
}
INIT_LIST_HEAD(&sma->pending_alter);
}
/**
* merge_queues - merge single semop queues into global queue
* @sma: semaphore array
*
* This function merges all per-semaphore queues into the global queue.
* It is necessary to achieve FIFO ordering for the pending single-sop
* operations when a multi-semop operation must sleep.
* Only the alter operations must be moved, the const operations can stay.
*/
static void merge_queues(struct sem_array *sma)
{
int i;
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *sem = sma->sem_base + i;
list_splice_init(&sem->pending_alter, &sma->pending_alter);
}
}
static void sem_rcu_free(struct rcu_head *head)
{
struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
struct sem_array *sma = ipc_rcu_to_struct(p);
security_sem_free(sma);
ipc_rcu_free(head);
}
/*
* spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
* are only control barriers.
* The code must pair with spin_unlock(&sem->lock) or
* spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
*
* smp_rmb() is sufficient, as writes cannot pass the control barrier.
*/
#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb()
/*
* Wait until all currently ongoing simple ops have completed.
* Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check
* that sem_perm.lock is free.
* that a) sem_perm.lock is free and b) complex_count is 0.
*/
static void sem_wait_array(struct sem_array *sma)
{
int i;
struct sem *sem;
if (sma->complex_count) {
/* The thread that increased sma->complex_count waited on
* all sem->lock locks. Thus we don't need to wait again.
*/
return;
}
for (i = 0; i < sma->sem_nsems; i++) {
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);
}
ipc_smp_acquire__after_spin_is_unlocked();
}
/*
* If the request contains only one semaphore operation, and there are
* no complex transactions pending, lock only the semaphore involved.
* Otherwise, lock the entire semaphore array, since we either have
* multiple semaphores in our own semops, or we need to look at
* semaphores from other pending complex operations.
*/
static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
int nsops)
{
struct sem *sem;
if (nsops != 1) {
/* Complex operation - acquire a full lock */
ipc_lock_object(&sma->sem_perm);
/* And wait until all simple ops that are processed
* right now have dropped their locks.
*/
sem_wait_array(sma);
return -1;
}
/*
* Only one semaphore affected - try to optimize locking.
* The rules are:
* - optimized locking is possible if no complex operation
* is either enqueued or processed right now.
* - The test for enqueued complex ops is simple:
* sma->complex_count != 0
* - Testing for complex ops that are processed right now is
* a bit more difficult. Complex ops acquire the full lock
* and first wait that the running simple ops have completed.
* (see above)
* Thus: If we own a simple lock and the global lock is free
* and complex_count is now 0, then it will stay 0 and
* thus just locking sem->lock is sufficient.
*/
sem = sma->sem_base + sops->sem_num;
if (sma->complex_count == 0) {
/*
* It appears that no complex operation is around.
* Acquire the per-semaphore lock.
*/
spin_lock(&sem->lock);
/* Then check that the global lock is free */
if (!spin_is_locked(&sma->sem_perm.lock)) {
/*
* We need a memory barrier with acquire semantics,
* otherwise we can race with another thread that does:
* complex_count++;
* spin_unlock(sem_perm.lock);
*/
ipc_smp_acquire__after_spin_is_unlocked();
/*
* Now repeat the test of complex_count:
* It can't change anymore until we drop sem->lock.
* Thus: if is now 0, then it will stay 0.
*/
if (sma->complex_count == 0) {
/* fast path successful! */
return sops->sem_num;
}
}
spin_unlock(&sem->lock);
}
/* slow path: acquire the full lock */
ipc_lock_object(&sma->sem_perm);
if (sma->complex_count == 0) {
/* False alarm:
* There is no complex operation, thus we can switch
* back to the fast path.
*/
spin_lock(&sem->lock);
ipc_unlock_object(&sma->sem_perm);
return sops->sem_num;
} else {
/* Not a false alarm, thus complete the sequence for a
* full lock.
*/
sem_wait_array(sma);
return -1;
}
}
static inline void sem_unlock(struct sem_array *sma, int locknum)
{
if (locknum == -1) {
unmerge_queues(sma);
ipc_unlock_object(&sma->sem_perm);
} else {
struct sem *sem = sma->sem_base + locknum;
spin_unlock(&sem->lock);
}
}
/*
* sem_lock_(check_) routines are called in the paths where the rwsem
* is not held.
*
* The caller holds the RCU read lock.
*/
static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns,
int id, struct sembuf *sops, int nsops, int *locknum)
{
struct kern_ipc_perm *ipcp;
struct sem_array *sma;
ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
sma = container_of(ipcp, struct sem_array, sem_perm);
*locknum = sem_lock(sma, sops, nsops);
/* ipc_rmid() may have already freed the ID while sem_lock
* was spinning: verify that the structure is still valid
*/
if (ipc_valid_object(ipcp))
return container_of(ipcp, struct sem_array, sem_perm);
sem_unlock(sma, *locknum);
return ERR_PTR(-EINVAL);
}
static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
int id)
{
struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
if (IS_ERR(ipcp))
return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);
}
static inline void sem_lock_and_putref(struct sem_array *sma)
{
sem_lock(sma, NULL, -1);
ipc_rcu_putref(sma, ipc_rcu_free);
}
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
{
ipc_rmid(&sem_ids(ns), &s->sem_perm);
}
/*
* Lockless wakeup algorithm:
* Without the check/retry algorithm a lockless wakeup is possible:
* - queue.status is initialized to -EINTR before blocking.
* - wakeup is performed by
* * unlinking the queue entry from the pending list
* * setting queue.status to IN_WAKEUP
* This is the notification for the blocked thread that a
* result value is imminent.
* * call wake_up_process
* * set queue.status to the final value.
* - the previously blocked thread checks queue.status:
* * if it's IN_WAKEUP, then it must wait until the value changes
* * if it's not -EINTR, then the operation was completed by
* update_queue. semtimedop can return queue.status without
* performing any operation on the sem array.
* * otherwise it must acquire the spinlock and check what's up.
*
* The two-stage algorithm is necessary to protect against the following
* races:
* - if queue.status is set after wake_up_process, then the woken up idle
* thread could race forward and try (and fail) to acquire sma->lock
* before update_queue had a chance to set queue.status
* - if queue.status is written before wake_up_process and if the
* blocked process is woken up by a signal between writing
* queue.status and the wake_up_process, then the woken up
* process could return from semtimedop and die by calling
* sys_exit before wake_up_process is called. Then wake_up_process
* will oops, because the task structure is already invalid.
* (yes, this happened on s390 with sysv msg).
*
*/
#define IN_WAKEUP 1
/**
* newary - Create a new semaphore set
* @ns: namespace
* @params: ptr to the structure that contains key, semflg and nsems
*
* Called with sem_ids.rwsem held (as a writer)
*/
static int newary(struct ipc_namespace *ns, struct ipc_params *params)
{
int id;
int retval;
struct sem_array *sma;
int size;
key_t key = params->key;
int nsems = params->u.nsems;
int semflg = params->flg;
int i;
if (!nsems)
return -EINVAL;
if (ns->used_sems + nsems > ns->sc_semmns)
return -ENOSPC;
size = sizeof(*sma) + nsems * sizeof(struct sem);
sma = ipc_rcu_alloc(size);
if (!sma)
return -ENOMEM;
memset(sma, 0, size);
sma->sem_perm.mode = (semflg & S_IRWXUGO);
sma->sem_perm.key = key;
sma->sem_perm.security = NULL;
retval = security_sem_alloc(sma);
if (retval) {
ipc_rcu_putref(sma, ipc_rcu_free);
return retval;
}
sma->sem_base = (struct sem *) &sma[1];
for (i = 0; i < nsems; i++) {
INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
spin_lock_init(&sma->sem_base[i].lock);
}
sma->complex_count = 0;
INIT_LIST_HEAD(&sma->pending_alter);
INIT_LIST_HEAD(&sma->pending_const);
INIT_LIST_HEAD(&sma->list_id);
sma->sem_nsems = nsems;
sma->sem_ctime = get_seconds();
id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
if (id < 0) {
ipc_rcu_putref(sma, sem_rcu_free);
return id;
}
ns->used_sems += nsems;
sem_unlock(sma, -1);
rcu_read_unlock();
return sma->sem_perm.id;
}
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
{
struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm);
return security_sem_associate(sma, semflg);
}
/*
* Called with sem_ids.rwsem and ipcp locked.
*/
static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
struct ipc_params *params)
{
struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm);
if (params->u.nsems > sma->sem_nsems)
return -EINVAL;
return 0;
}
SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
{
struct ipc_namespace *ns;
static const struct ipc_ops sem_ops = {
.getnew = newary,
.associate = sem_security,
.more_checks = sem_more_checks,
};
struct ipc_params sem_params;
ns = current->nsproxy->ipc_ns;
if (nsems < 0 || nsems > ns->sc_semmsl)
return -EINVAL;
sem_params.key = key;
sem_params.flg = semflg;
sem_params.u.nsems = nsems;
return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
}
/**
* perform_atomic_semop - Perform (if possible) a semaphore operation
* @sma: semaphore array
* @q: struct sem_queue that describes the operation
*
* Returns 0 if the operation was possible.
* Returns 1 if the operation is impossible, the caller must sleep.
* Negative values are error codes.
*/
static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
{
int result, sem_op, nsops, pid;
struct sembuf *sop;
struct sem *curr;
struct sembuf *sops;
struct sem_undo *un;
sops = q->sops;
nsops = q->nsops;
un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) {
curr = sma->sem_base + sop->sem_num;
sem_op = sop->sem_op;
result = curr->semval;
if (!sem_op && result)
goto would_block;
result += sem_op;
if (result < 0)
goto would_block;
if (result > SEMVMX)
goto out_of_range;
if (sop->sem_flg & SEM_UNDO) {
int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
goto out_of_range;
un->semadj[sop->sem_num] = undo;
}
curr->semval = result;
}
sop--;
pid = q->pid;
while (sop >= sops) {
sma->sem_base[sop->sem_num].sempid = pid;
sop--;
}
return 0;
out_of_range:
result = -ERANGE;
goto undo;
would_block:
q->blocking = sop;
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
undo:
sop--;
while (sop >= sops) {
sem_op = sop->sem_op;
sma->sem_base[sop->sem_num].semval -= sem_op;
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] += sem_op;
sop--;
}
return result;
}
/** wake_up_sem_queue_prepare(q, error): Prepare wake-up
* @q: queue entry that must be signaled
* @error: Error value for the signal
*
* Prepare the wake-up of the queue entry q.
*/
static void wake_up_sem_queue_prepare(struct list_head *pt,
struct sem_queue *q, int error)
{
if (list_empty(pt)) {
/*
* Hold preempt off so that we don't get preempted and have the
* wakee busy-wait until we're scheduled back on.
*/
preempt_disable();
}
q->status = IN_WAKEUP;
q->pid = error;
list_add_tail(&q->list, pt);
}
/**
* wake_up_sem_queue_do - do the actual wake-up
* @pt: list of tasks to be woken up
*
* Do the actual wake-up.
* The function is called without any locks held, thus the semaphore array
* could be destroyed already and the tasks can disappear as soon as the
* status is set to the actual return code.
*/
static void wake_up_sem_queue_do(struct list_head *pt)
{
struct sem_queue *q, *t;
int did_something;
did_something = !list_empty(pt);
list_for_each_entry_safe(q, t, pt, list) {
wake_up_process(q->sleeper);
/* q can disappear immediately after writing q->status. */
smp_wmb();
q->status = q->pid;
}
if (did_something)
preempt_enable();
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
{
list_del(&q->list);
if (q->nsops > 1)
sma->complex_count--;
}
/** check_restart(sma, q)
* @sma: semaphore array
* @q: the operation that just completed
*
* update_queue is O(N^2) when it restarts scanning the whole queue of
* waiting operations. Therefore this function checks if the restart is
* really necessary. It is called after a previously waiting operation
* modified the array.
* Note that wait-for-zero operations are handled without restart.
*/
static int check_restart(struct sem_array *sma, struct sem_queue *q)
{
/* pending complex alter operations are too difficult to analyse */
if (!list_empty(&sma->pending_alter))
return 1;
/* we were a sleeping complex operation. Too difficult */
if (q->nsops > 1)
return 1;
/* It is impossible that someone waits for the new value:
* - complex operations always restart.
* - wait-for-zero are handled seperately.
* - q is a previously sleeping simple operation that
* altered the array. It must be a decrement, because
* simple increments never sleep.
* - If there are older (higher priority) decrements
* in the queue, then they have observed the original
* semval value and couldn't proceed. The operation
* decremented to value - thus they won't proceed either.
*/
return 0;
}
/**
* wake_const_ops - wake up non-alter tasks
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @pt: list head for the tasks that must be woken up.
*
* wake_const_ops must be called after a semaphore in a semaphore array
* was set to 0. If complex const operations are pending, wake_const_ops must
* be called with semnum = -1, as well as with the number of each modified
* semaphore.
* The tasks that must be woken up are added to @pt. The return code
* is stored in q->pid.
* The function returns 1 if at least one operation was completed successfully.
*/
static int wake_const_ops(struct sem_array *sma, int semnum,
struct list_head *pt)
{
struct sem_queue *q;
struct list_head *walk;
struct list_head *pending_list;
int semop_completed = 0;
if (semnum == -1)
pending_list = &sma->pending_const;
else
pending_list = &sma->sem_base[semnum].pending_const;
walk = pending_list->next;
while (walk != pending_list) {
int error;
q = container_of(walk, struct sem_queue, list);
walk = walk->next;
error = perform_atomic_semop(sma, q);
if (error <= 0) {
/* operation completed, remove from queue & wakeup */
unlink_queue(sma, q);
wake_up_sem_queue_prepare(pt, q, error);
if (error == 0)
semop_completed = 1;
}
}
return semop_completed;
}
/**
* do_smart_wakeup_zero - wakeup all wait for zero tasks
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @pt: list head of the tasks that must be woken up.
*
* Checks all required queue for wait-for-zero operations, based
* on the actual changes that were performed on the semaphore array.
* The function returns 1 if at least one operation was completed successfully.
*/
static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
int nsops, struct list_head *pt)
{
int i;
int semop_completed = 0;
int got_zero = 0;
/* first: the per-semaphore queues, if known */
if (sops) {
for (i = 0; i < nsops; i++) {
int num = sops[i].sem_num;
if (sma->sem_base[num].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, num, pt);
}
}
} else {
/*
* No sops means modified semaphores not known.
* Assume all were changed.
*/
for (i = 0; i < sma->sem_nsems; i++) {
if (sma->sem_base[i].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, i, pt);
}
}
}
/*
* If one of the modified semaphores got 0,
* then check the global queue, too.
*/
if (got_zero)
semop_completed |= wake_const_ops(sma, -1, pt);
return semop_completed;
}
/**
* update_queue - look for tasks that can be completed.
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @pt: list head for the tasks that must be woken up.
*
* update_queue must be called after a semaphore in a semaphore array
* was modified. If multiple semaphores were modified, update_queue must
* be called with semnum = -1, as well as with the number of each modified
* semaphore.
* The tasks that must be woken up are added to @pt. The return code
* is stored in q->pid.
* The function internally checks if const operations can now succeed.
*
* The function return 1 if at least one semop was completed successfully.
*/
static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
{
struct sem_queue *q;
struct list_head *walk;
struct list_head *pending_list;
int semop_completed = 0;
if (semnum == -1)
pending_list = &sma->pending_alter;
else
pending_list = &sma->sem_base[semnum].pending_alter;
again:
walk = pending_list->next;
while (walk != pending_list) {
int error, restart;
q = container_of(walk, struct sem_queue, list);
walk = walk->next;
/* If we are scanning the single sop, per-semaphore list of
* one semaphore and that semaphore is 0, then it is not
* necessary to scan further: simple increments
* that affect only one entry succeed immediately and cannot
* be in the per semaphore pending queue, and decrements
* cannot be successful if the value is already 0.
*/
if (semnum != -1 && sma->sem_base[semnum].semval == 0)
break;
error = perform_atomic_semop(sma, q);
/* Does q->sleeper still need to sleep? */
if (error > 0)
continue;
unlink_queue(sma, q);
if (error) {
restart = 0;
} else {
semop_completed = 1;
do_smart_wakeup_zero(sma, q->sops, q->nsops, pt);
restart = check_restart(sma, q);
}
wake_up_sem_queue_prepare(pt, q, error);
if (restart)
goto again;
}
return semop_completed;
}
/**
* set_semotime - set sem_otime
* @sma: semaphore array
* @sops: operations that modified the array, may be NULL
*
* sem_otime is replicated to avoid cache line trashing.
* This function sets one instance to the current time.
*/
static void set_semotime(struct sem_array *sma, struct sembuf *sops)
{
if (sops == NULL) {
sma->sem_base[0].sem_otime = get_seconds();
} else {
sma->sem_base[sops[0].sem_num].sem_otime =
get_seconds();
}
}
/**
* do_smart_update - optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @otime: force setting otime
* @pt: list head of the tasks that must be woken up.
*
* do_smart_update() does the required calls to update_queue and wakeup_zero,
* based on the actual changes that were performed on the semaphore array.
* Note that the function does not do the actual wake-up: the caller is
* responsible for calling wake_up_sem_queue_do(@pt).
* It is safe to perform this call after dropping all locks.
*/
static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
int otime, struct list_head *pt)
{
int i;
otime |= do_smart_wakeup_zero(sma, sops, nsops, pt);
if (!list_empty(&sma->pending_alter)) {
/* semaphore array uses the global queue - just process it. */
otime |= update_queue(sma, -1, pt);
} else {
if (!sops) {
/*
* No sops, thus the modified semaphores are not
* known. Check all.
*/
for (i = 0; i < sma->sem_nsems; i++)
otime |= update_queue(sma, i, pt);
} else {
/*
* Check the semaphores that were increased:
* - No complex ops, thus all sleeping ops are
* decrease.
* - if we decreased the value, then any sleeping
* semaphore ops wont be able to run: If the
* previous value was too small, then the new
* value will be too small, too.
*/
for (i = 0; i < nsops; i++) {
if (sops[i].sem_op > 0) {
otime |= update_queue(sma,
sops[i].sem_num, pt);
}
}
}
}
if (otime)
set_semotime(sma, sops);
}
/*
* check_qop: Test if a queued operation sleeps on the semaphore semnum
*/
static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
bool count_zero)
{
struct sembuf *sop = q->blocking;
/*
* Linux always (since 0.99.10) reported a task as sleeping on all
* semaphores. This violates SUS, therefore it was changed to the
* standard compliant behavior.
* Give the administrators a chance to notice that an application
* might misbehave because it relies on the Linux behavior.
*/
pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n"
"The task %s (%d) triggered the difference, watch for misbehavior.\n",
current->comm, task_pid_nr(current));
if (sop->sem_num != semnum)
return 0;
if (count_zero && sop->sem_op == 0)
return 1;
if (!count_zero && sop->sem_op < 0)
return 1;
return 0;
}
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
*
* Per definition, a task waits only on the semaphore of the first semop
* that cannot proceed, even if additional operation would block, too.
*/
static int count_semcnt(struct sem_array *sma, ushort semnum,
bool count_zero)
{
struct list_head *l;
struct sem_queue *q;
int semcnt;
semcnt = 0;
/* First: check the simple operations. They are easy to evaluate */
if (count_zero)
l = &sma->sem_base[semnum].pending_const;
else
l = &sma->sem_base[semnum].pending_alter;
list_for_each_entry(q, l, list) {
/* all task on a per-semaphore list sleep on exactly
* that semaphore
*/
semcnt++;
}
/* Then: check the complex operations. */
list_for_each_entry(q, &sma->pending_alter, list) {
semcnt += check_qop(sma, semnum, q, count_zero);
}
if (count_zero) {
list_for_each_entry(q, &sma->pending_const, list) {
semcnt += check_qop(sma, semnum, q, count_zero);
}
}
return semcnt;
}
/* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
* as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem
* remains locked on exit.
*/
static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
struct sem_undo *un, *tu;
struct sem_queue *q, *tq;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
struct list_head tasks;
int i;
/* Free the existing undo structures for this semaphore set. */
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
list_del(&un->list_id);
spin_lock(&un->ulp->lock);
un->semid = -1;
list_del_rcu(&un->list_proc);
spin_unlock(&un->ulp->lock);
kfree_rcu(un, rcu);
}
/* Wake up all pending processes and let them fail with EIDRM. */
INIT_LIST_HEAD(&tasks);
list_for_each_entry_safe(q, tq, &sma->pending_const, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *sem = sma->sem_base + i;
list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
list_for_each_entry_safe(q, tq, &sem->pending_alter, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
}
/* Remove the semaphore set from the IDR */
sem_rmid(ns, sma);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
ns->used_sems -= sma->sem_nsems;
ipc_rcu_putref(sma, sem_rcu_free);
}
static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
{
switch (version) {
case IPC_64:
return copy_to_user(buf, in, sizeof(*in));
case IPC_OLD:
{
struct semid_ds out;
memset(&out, 0, sizeof(out));
ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
out.sem_otime = in->sem_otime;
out.sem_ctime = in->sem_ctime;
out.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &out, sizeof(out));
}
default:
return -EINVAL;
}
}
static time_t get_semotime(struct sem_array *sma)
{
int i;
time_t res;
res = sma->sem_base[0].sem_otime;
for (i = 1; i < sma->sem_nsems; i++) {
time_t to = sma->sem_base[i].sem_otime;
if (to > res)
res = to;
}
return res;
}
static int semctl_nolock(struct ipc_namespace *ns, int semid,
int cmd, int version, void __user *p)
{
int err;
struct sem_array *sma;
switch (cmd) {
case IPC_INFO:
case SEM_INFO:
{
struct seminfo seminfo;
int max_id;
err = security_sem_semctl(NULL, cmd);
if (err)
return err;
memset(&seminfo, 0, sizeof(seminfo));
seminfo.semmni = ns->sc_semmni;
seminfo.semmns = ns->sc_semmns;
seminfo.semmsl = ns->sc_semmsl;
seminfo.semopm = ns->sc_semopm;
seminfo.semvmx = SEMVMX;
seminfo.semmnu = SEMMNU;
seminfo.semmap = SEMMAP;
seminfo.semume = SEMUME;
down_read(&sem_ids(ns).rwsem);
if (cmd == SEM_INFO) {
seminfo.semusz = sem_ids(ns).in_use;
seminfo.semaem = ns->used_sems;
} else {
seminfo.semusz = SEMUSZ;
seminfo.semaem = SEMAEM;
}
max_id = ipc_get_maxid(&sem_ids(ns));
up_read(&sem_ids(ns).rwsem);
if (copy_to_user(p, &seminfo, sizeof(struct seminfo)))
return -EFAULT;
return (max_id < 0) ? 0 : max_id;
}
case IPC_STAT:
case SEM_STAT:
{
struct semid64_ds tbuf;
int id = 0;
memset(&tbuf, 0, sizeof(tbuf));
rcu_read_lock();
if (cmd == SEM_STAT) {
sma = sem_obtain_object(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
id = sma->sem_perm.id;
} else {
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
}
err = -EACCES;
if (ipcperms(ns, &sma->sem_perm, S_IRUGO))
goto out_unlock;
err = security_sem_semctl(sma, cmd);
if (err)
goto out_unlock;
kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
tbuf.sem_otime = get_semotime(sma);
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
rcu_read_unlock();
if (copy_semid_to_user(p, &tbuf, version))
return -EFAULT;
return id;
}
default:
return -EINVAL;
}
out_unlock:
rcu_read_unlock();
return err;
}
static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
unsigned long arg)
{
struct sem_undo *un;
struct sem_array *sma;
struct sem *curr;
int err;
struct list_head tasks;
int val;
#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
/* big-endian 64bit */
val = arg >> 32;
#else
/* 32bit or little-endian 64bit */
val = arg;
#endif
if (val > SEMVMX || val < 0)
return -ERANGE;
INIT_LIST_HEAD(&tasks);
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return PTR_ERR(sma);
}
if (semnum < 0 || semnum >= sma->sem_nsems) {
rcu_read_unlock();
return -EINVAL;
}
if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) {
rcu_read_unlock();
return -EACCES;
}
err = security_sem_semctl(sma, SETVAL);
if (err) {
rcu_read_unlock();
return -EACCES;
}
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
return -EIDRM;
}
curr = &sma->sem_base[semnum];
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id)
un->semadj[semnum] = 0;
curr->semval = val;
curr->sempid = task_tgid_vnr(current);
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
do_smart_update(sma, NULL, 0, 0, &tasks);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
return 0;
}
static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int cmd, void __user *p)
{
struct sem_array *sma;
struct sem *curr;
int err, nsems;
ushort fast_sem_io[SEMMSL_FAST];
ushort *sem_io = fast_sem_io;
struct list_head tasks;
INIT_LIST_HEAD(&tasks);
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return PTR_ERR(sma);
}
nsems = sma->sem_nsems;
err = -EACCES;
if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO))
goto out_rcu_wakeup;
err = security_sem_semctl(sma, cmd);
if (err)
goto out_rcu_wakeup;
err = -EACCES;
switch (cmd) {
case GETALL:
{
ushort __user *array = p;
int i;
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
if (nsems > SEMMSL_FAST) {
if (!ipc_rcu_getref(sma)) {
err = -EIDRM;
goto out_unlock;
}
sem_unlock(sma, -1);
rcu_read_unlock();
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if (sem_io == NULL) {
ipc_rcu_putref(sma, ipc_rcu_free);
return -ENOMEM;
}
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
}
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sem_base[i].semval;
sem_unlock(sma, -1);
rcu_read_unlock();
err = 0;
if (copy_to_user(array, sem_io, nsems*sizeof(ushort)))
err = -EFAULT;
goto out_free;
}
case SETALL:
{
int i;
struct sem_undo *un;
if (!ipc_rcu_getref(sma)) {
err = -EIDRM;
goto out_rcu_wakeup;
}
rcu_read_unlock();
if (nsems > SEMMSL_FAST) {
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if (sem_io == NULL) {
ipc_rcu_putref(sma, ipc_rcu_free);
return -ENOMEM;
}
}
if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
ipc_rcu_putref(sma, ipc_rcu_free);
err = -EFAULT;
goto out_free;
}
for (i = 0; i < nsems; i++) {
if (sem_io[i] > SEMVMX) {
ipc_rcu_putref(sma, ipc_rcu_free);
err = -ERANGE;
goto out_free;
}
}
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
for (i = 0; i < nsems; i++) {
sma->sem_base[i].semval = sem_io[i];
sma->sem_base[i].sempid = task_tgid_vnr(current);
}
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id) {
for (i = 0; i < nsems; i++)
un->semadj[i] = 0;
}
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
do_smart_update(sma, NULL, 0, 0, &tasks);
err = 0;
goto out_unlock;
}
/* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
}
err = -EINVAL;
if (semnum < 0 || semnum >= nsems)
goto out_rcu_wakeup;
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
curr = &sma->sem_base[semnum];
switch (cmd) {
case GETVAL:
err = curr->semval;
goto out_unlock;
case GETPID:
err = curr->sempid;
goto out_unlock;
case GETNCNT:
err = count_semcnt(sma, semnum, 0);
goto out_unlock;
case GETZCNT:
err = count_semcnt(sma, semnum, 1);
goto out_unlock;
}
out_unlock:
sem_unlock(sma, -1);
out_rcu_wakeup:
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
out_free:
if (sem_io != fast_sem_io)
ipc_free(sem_io);
return err;
}
static inline unsigned long
copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
{
switch (version) {
case IPC_64:
if (copy_from_user(out, buf, sizeof(*out)))
return -EFAULT;
return 0;
case IPC_OLD:
{
struct semid_ds tbuf_old;
if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
return -EFAULT;
out->sem_perm.uid = tbuf_old.sem_perm.uid;
out->sem_perm.gid = tbuf_old.sem_perm.gid;
out->sem_perm.mode = tbuf_old.sem_perm.mode;
return 0;
}
default:
return -EINVAL;
}
}
/*
* This function handles some semctl commands which require the rwsem
* to be held in write mode.
* NOTE: no locks must be held, the rwsem is taken inside this function.
*/
static int semctl_down(struct ipc_namespace *ns, int semid,
int cmd, int version, void __user *p)
{
struct sem_array *sma;
int err;
struct semid64_ds semid64;
struct kern_ipc_perm *ipcp;
if (cmd == IPC_SET) {
if (copy_semid_from_user(&semid64, p, version))
return -EFAULT;
}
down_write(&sem_ids(ns).rwsem);
rcu_read_lock();
ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
&semid64.sem_perm, 0);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
goto out_unlock1;
}
sma = container_of(ipcp, struct sem_array, sem_perm);
err = security_sem_semctl(sma, cmd);
if (err)
goto out_unlock1;
switch (cmd) {
case IPC_RMID:
sem_lock(sma, NULL, -1);
/* freeary unlocks the ipc object and rcu */
freeary(ns, ipcp);
goto out_up;
case IPC_SET:
sem_lock(sma, NULL, -1);
err = ipc_update_perm(&semid64.sem_perm, ipcp);
if (err)
goto out_unlock0;
sma->sem_ctime = get_seconds();
break;
default:
err = -EINVAL;
goto out_unlock1;
}
out_unlock0:
sem_unlock(sma, -1);
out_unlock1:
rcu_read_unlock();
out_up:
up_write(&sem_ids(ns).rwsem);
return err;
}
SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg)
{
int version;
struct ipc_namespace *ns;
void __user *p = (void __user *)arg;
if (semid < 0)
return -EINVAL;
version = ipc_parse_version(&cmd);
ns = current->nsproxy->ipc_ns;
switch (cmd) {
case IPC_INFO:
case SEM_INFO:
case IPC_STAT:
case SEM_STAT:
return semctl_nolock(ns, semid, cmd, version, p);
case GETALL:
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case SETALL:
return semctl_main(ns, semid, semnum, cmd, p);
case SETVAL:
return semctl_setval(ns, semid, semnum, arg);
case IPC_RMID:
case IPC_SET:
return semctl_down(ns, semid, cmd, version, p);
default:
return -EINVAL;
}
}
/* If the task doesn't already have a undo_list, then allocate one
* here. We guarantee there is only one thread using this undo list,
* and current is THE ONE
*
* If this allocation and assignment succeeds, but later
* portions of this code fail, there is no need to free the sem_undo_list.
* Just let it stay associated with the task, and it'll be freed later
* at exit time.
*
* This can block, so callers must hold no locks.
*/
static inline int get_undo_list(struct sem_undo_list **undo_listp)
{
struct sem_undo_list *undo_list;
undo_list = current->sysvsem.undo_list;
if (!undo_list) {
undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
if (undo_list == NULL)
return -ENOMEM;
spin_lock_init(&undo_list->lock);
atomic_set(&undo_list->refcnt, 1);
INIT_LIST_HEAD(&undo_list->list_proc);
current->sysvsem.undo_list = undo_list;
}
*undo_listp = undo_list;
return 0;
}
static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
{
struct sem_undo *un;
list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
if (un->semid == semid)
return un;
}
return NULL;
}
static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
{
struct sem_undo *un;
assert_spin_locked(&ulp->lock);
un = __lookup_undo(ulp, semid);
if (un) {
list_del_rcu(&un->list_proc);
list_add_rcu(&un->list_proc, &ulp->list_proc);
}
return un;
}
/**
* find_alloc_undo - lookup (and if not present create) undo array
* @ns: namespace
* @semid: semaphore array id
*
* The function looks up (and if not present creates) the undo structure.
* The size of the undo structure depends on the size of the semaphore
* array, thus the alloc path is not that straightforward.
* Lifetime-rules: sem_undo is rcu-protected, on success, the function
* performs a rcu_read_lock().
*/
static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
{
struct sem_array *sma;
struct sem_undo_list *ulp;
struct sem_undo *un, *new;
int nsems, error;
error = get_undo_list(&ulp);
if (error)
return ERR_PTR(error);
rcu_read_lock();
spin_lock(&ulp->lock);
un = lookup_undo(ulp, semid);
spin_unlock(&ulp->lock);
if (likely(un != NULL))
goto out;
/* no undo structure around - allocate one. */
/* step 1: figure out the size of the semaphore array */
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return ERR_CAST(sma);
}
nsems = sma->sem_nsems;
if (!ipc_rcu_getref(sma)) {
rcu_read_unlock();
un = ERR_PTR(-EIDRM);
goto out;
}
rcu_read_unlock();
/* step 2: allocate new undo structure */
new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
if (!new) {
ipc_rcu_putref(sma, ipc_rcu_free);
return ERR_PTR(-ENOMEM);
}
/* step 3: Acquire the lock on semaphore array */
rcu_read_lock();
sem_lock_and_putref(sma);
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
kfree(new);
un = ERR_PTR(-EIDRM);
goto out;
}
spin_lock(&ulp->lock);
/*
* step 4: check for races: did someone else allocate the undo struct?
*/
un = lookup_undo(ulp, semid);
if (un) {
kfree(new);
goto success;
}
/* step 5: initialize & link new undo structure */
new->semadj = (short *) &new[1];
new->ulp = ulp;
new->semid = semid;
assert_spin_locked(&ulp->lock);
list_add_rcu(&new->list_proc, &ulp->list_proc);
ipc_assert_locked_object(&sma->sem_perm);
list_add(&new->list_id, &sma->list_id);
un = new;
success:
spin_unlock(&ulp->lock);
sem_unlock(sma, -1);
out:
return un;
}
/**
* get_queue_result - retrieve the result code from sem_queue
* @q: Pointer to queue structure
*
* Retrieve the return code from the pending queue. If IN_WAKEUP is found in
* q->status, then we must loop until the value is replaced with the final
* value: This may happen if a task is woken up by an unrelated event (e.g.
* signal) and in parallel the task is woken up by another task because it got
* the requested semaphores.
*
* The function can be called with or without holding the semaphore spinlock.
*/
static int get_queue_result(struct sem_queue *q)
{
int error;
error = q->status;
while (unlikely(error == IN_WAKEUP)) {
cpu_relax();
error = q->status;
}
return error;
}
SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
unsigned, nsops, const struct timespec __user *, timeout)
{
int error = -EINVAL;
struct sem_array *sma;
struct sembuf fast_sops[SEMOPM_FAST];
struct sembuf *sops = fast_sops, *sop;
struct sem_undo *un;
int undos = 0, alter = 0, max, locknum;
struct sem_queue queue;
unsigned long jiffies_left = 0;
struct ipc_namespace *ns;
struct list_head tasks;
ns = current->nsproxy->ipc_ns;
if (nsops < 1 || semid < 0)
return -EINVAL;
if (nsops > ns->sc_semopm)
return -E2BIG;
if (nsops > SEMOPM_FAST) {
sops = kmalloc(sizeof(*sops)*nsops, GFP_KERNEL);
if (sops == NULL)
return -ENOMEM;
}
if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
error = -EFAULT;
goto out_free;
}
if (timeout) {
struct timespec _timeout;
if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
error = -EFAULT;
goto out_free;
}
if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
_timeout.tv_nsec >= 1000000000L) {
error = -EINVAL;
goto out_free;
}
jiffies_left = timespec_to_jiffies(&_timeout);
}
max = 0;
for (sop = sops; sop < sops + nsops; sop++) {
if (sop->sem_num >= max)
max = sop->sem_num;
if (sop->sem_flg & SEM_UNDO)
undos = 1;
if (sop->sem_op != 0)
alter = 1;
}
INIT_LIST_HEAD(&tasks);
if (undos) {
/* On success, find_alloc_undo takes the rcu_read_lock */
un = find_alloc_undo(ns, semid);
if (IS_ERR(un)) {
error = PTR_ERR(un);
goto out_free;
}
} else {
un = NULL;
rcu_read_lock();
}
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
error = PTR_ERR(sma);
goto out_free;
}
error = -EFBIG;
if (max >= sma->sem_nsems)
goto out_rcu_wakeup;
error = -EACCES;
if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
goto out_rcu_wakeup;
error = security_sem_semop(sma, sops, nsops, alter);
if (error)
goto out_rcu_wakeup;
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
/*
* We eventually might perform the following check in a lockless
* fashion, considering ipc_valid_object() locking constraints.
* If nsops == 1 and there is no contention for sem_perm.lock, then
* only a per-semaphore lock is held and it's OK to proceed with the
* check below. More details on the fine grained locking scheme
* entangled here and why it's RMID race safe on comments at sem_lock()
*/
if (!ipc_valid_object(&sma->sem_perm))
goto out_unlock_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
* and now a new array with received the same id. Check and fail.
* This case can be detected checking un->semid. The existence of
* "un" itself is guaranteed by rcu.
*/
if (un && un->semid == -1)
goto out_unlock_free;
queue.sops = sops;
queue.nsops = nsops;
queue.undo = un;
queue.pid = task_tgid_vnr(current);
queue.alter = alter;
error = perform_atomic_semop(sma, &queue);
if (error == 0) {
/* If the operation was successful, then do
* the required updates.
*/
if (alter)
do_smart_update(sma, sops, nsops, 1, &tasks);
else
set_semotime(sma, sops);
}
if (error <= 0)
goto out_unlock_free;
/* We need to sleep on this operation, so we put the current
* task into the pending queue and go to sleep.
*/
if (nsops == 1) {
struct sem *curr;
curr = &sma->sem_base[sops->sem_num];
if (alter) {
if (sma->complex_count) {
list_add_tail(&queue.list,
&sma->pending_alter);
} else {
list_add_tail(&queue.list,
&curr->pending_alter);
}
} else {
list_add_tail(&queue.list, &curr->pending_const);
}
} else {
if (!sma->complex_count)
merge_queues(sma);
if (alter)
list_add_tail(&queue.list, &sma->pending_alter);
else
list_add_tail(&queue.list, &sma->pending_const);
sma->complex_count++;
}
queue.status = -EINTR;
queue.sleeper = current;
sleep_again:
__set_current_state(TASK_INTERRUPTIBLE);
sem_unlock(sma, locknum);
rcu_read_unlock();
if (timeout)
jiffies_left = schedule_timeout(jiffies_left);
else
schedule();
error = get_queue_result(&queue);
if (error != -EINTR) {
/* fast path: update_queue already obtained all requested
* resources.
* Perform a smp_mb(): User space could assume that semop()
* is a memory barrier: Without the mb(), the cpu could
* speculatively read in user space stale data that was
* overwritten by the previous owner of the semaphore.
*/
smp_mb();
goto out_free;
}
rcu_read_lock();
sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum);
/*
* Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
*/
error = get_queue_result(&queue);
/*
* Array removed? If yes, leave without sem_unlock().
*/
if (IS_ERR(sma)) {
rcu_read_unlock();
goto out_free;
}
/*
* If queue.status != -EINTR we are woken up by another process.
* Leave without unlink_queue(), but with sem_unlock().
*/
if (error != -EINTR)
goto out_unlock_free;
/*
* If an interrupt occurred we have to clean up the queue
*/
if (timeout && jiffies_left == 0)
error = -EAGAIN;
/*
* If the wakeup was spurious, just retry
*/
if (error == -EINTR && !signal_pending(current))
goto sleep_again;
unlink_queue(sma, &queue);
out_unlock_free:
sem_unlock(sma, locknum);
out_rcu_wakeup:
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
out_free:
if (sops != fast_sops)
kfree(sops);
return error;
}
SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops,
unsigned, nsops)
{
return sys_semtimedop(semid, tsops, nsops, NULL);
}
/* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
* parent and child tasks.
*/
int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
{
struct sem_undo_list *undo_list;
int error;
if (clone_flags & CLONE_SYSVSEM) {
error = get_undo_list(&undo_list);
if (error)
return error;
atomic_inc(&undo_list->refcnt);
tsk->sysvsem.undo_list = undo_list;
} else
tsk->sysvsem.undo_list = NULL;
return 0;
}
/*
* add semadj values to semaphores, free undo structures.
* undo structures are not freed when semaphore arrays are destroyed
* so some of them may be out of date.
* IMPLEMENTATION NOTE: There is some confusion over whether the
* set of adjustments that needs to be done should be done in an atomic
* manner or not. That is, if we are attempting to decrement the semval
* should we queue up and wait until we can do so legally?
* The original implementation attempted to do this (queue and wait).
* The current implementation does not do so. The POSIX standard
* and SVID should be consulted to determine what behavior is mandated.
*/
void exit_sem(struct task_struct *tsk)
{
struct sem_undo_list *ulp;
ulp = tsk->sysvsem.undo_list;
if (!ulp)
return;
tsk->sysvsem.undo_list = NULL;
if (!atomic_dec_and_test(&ulp->refcnt))
return;
for (;;) {
struct sem_array *sma;
struct sem_undo *un;
struct list_head tasks;
int semid, i;
rcu_read_lock();
un = list_entry_rcu(ulp->list_proc.next,
struct sem_undo, list_proc);
if (&un->list_proc == &ulp->list_proc) {
/*
* We must wait for freeary() before freeing this ulp,
* in case we raced with last sem_undo. There is a small
* possibility where we exit while freeary() didn't
* finish unlocking sem_undo_list.
*/
spin_unlock_wait(&ulp->lock);
rcu_read_unlock();
break;
}
spin_lock(&ulp->lock);
semid = un->semid;
spin_unlock(&ulp->lock);
/* exit_sem raced with IPC_RMID, nothing to do */
if (semid == -1) {
rcu_read_unlock();
continue;
}
sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
/* exit_sem raced with IPC_RMID, nothing to do */
if (IS_ERR(sma)) {
rcu_read_unlock();
continue;
}
sem_lock(sma, NULL, -1);
/* exit_sem raced with IPC_RMID, nothing to do */
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
}
un = __lookup_undo(ulp, semid);
if (un == NULL) {
/* exit_sem raced with IPC_RMID+semget() that created
* exactly the same semid. Nothing to do.
*/
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
}
/* remove un from the linked lists */
ipc_assert_locked_object(&sma->sem_perm);
list_del(&un->list_id);
/* we are the last process using this ulp, acquiring ulp->lock
* isn't required. Besides that, we are also protected against
* IPC_RMID as we hold sma->sem_perm lock now
*/
list_del_rcu(&un->list_proc);
/* perform adjustments registered in un */
for (i = 0; i < sma->sem_nsems; i++) {
struct sem *semaphore = &sma->sem_base[i];
if (un->semadj[i]) {
semaphore->semval += un->semadj[i];
/*
* Range checks of the new semaphore value,
* not defined by sus:
* - Some unices ignore the undo entirely
* (e.g. HP UX 11i 11.22, Tru64 V5.1)
* - some cap the value (e.g. FreeBSD caps
* at 0, but doesn't enforce SEMVMX)
*
* Linux caps the semaphore value, both at 0
* and at SEMVMX.
*
* Manfred <manfred@colorfullife.com>
*/
if (semaphore->semval < 0)
semaphore->semval = 0;
if (semaphore->semval > SEMVMX)
semaphore->semval = SEMVMX;
semaphore->sempid = task_tgid_vnr(current);
}
}
/* maybe some queued-up processes were waiting for this */
INIT_LIST_HEAD(&tasks);
do_smart_update(sma, NULL, 0, 1, &tasks);
sem_unlock(sma, -1);
rcu_read_unlock();
wake_up_sem_queue_do(&tasks);
kfree_rcu(un, rcu);
}
kfree(ulp);
}
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
struct user_namespace *user_ns = seq_user_ns(s);
struct sem_array *sma = it;
time_t sem_otime;
/*
* The proc interface isn't aware of sem_lock(), it calls
* ipc_lock_object() directly (in sysvipc_find_ipc).
* In order to stay compatible with sem_lock(), we must wait until
* all simple semop() calls have left their critical regions.
*/
sem_wait_array(sma);
sem_otime = get_semotime(sma);
seq_printf(s,
"%10d %10d %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
sma->sem_perm.key,
sma->sem_perm.id,
sma->sem_perm.mode,
sma->sem_nsems,
from_kuid_munged(user_ns, sma->sem_perm.uid),
from_kgid_munged(user_ns, sma->sem_perm.gid),
from_kuid_munged(user_ns, sma->sem_perm.cuid),
from_kgid_munged(user_ns, sma->sem_perm.cgid),
sem_otime,
sma->sem_ctime);
return 0;
}
#endif