linux/block/ioprio.c

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// SPDX-License-Identifier: GPL-2.0
/*
* fs/ioprio.c
*
* Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
*
* Helper functions for setting/querying io priorities of processes. The
* system calls closely mimmick getpriority/setpriority, see the man page for
* those. The prio argument is a composite of prio class and prio data, where
* the data argument has meaning within that class. The standard scheduling
* classes have 8 distinct prio levels, with 0 being the highest prio and 7
* being the lowest.
*
* IOW, setting BE scheduling class with prio 2 is done ala:
*
* unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
*
* ioprio_set(PRIO_PROCESS, pid, prio);
*
* See also Documentation/block/ioprio.rst
*
*/
include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-24 08:04:11 +00:00
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/ioprio.h>
#include <linux/cred.h>
#include <linux/blkdev.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/pid_namespace.h>
int ioprio_check_cap(int ioprio)
{
int class = IOPRIO_PRIO_CLASS(ioprio);
int data = IOPRIO_PRIO_DATA(ioprio);
switch (class) {
case IOPRIO_CLASS_RT:
/*
* Originally this only checked for CAP_SYS_ADMIN,
* which was implicitly allowed for pid 0 by security
* modules such as SELinux. Make sure we check
* CAP_SYS_ADMIN first to avoid a denial/avc for
* possibly missing CAP_SYS_NICE permission.
*/
if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
return -EPERM;
fallthrough;
/* rt has prio field too */
case IOPRIO_CLASS_BE:
if (data >= IOPRIO_NR_LEVELS || data < 0)
return -EINVAL;
break;
case IOPRIO_CLASS_IDLE:
break;
case IOPRIO_CLASS_NONE:
if (data)
return -EINVAL;
break;
default:
return -EINVAL;
}
return 0;
}
SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
{
struct task_struct *p, *g;
struct user_struct *user;
struct pid *pgrp;
kuid_t uid;
int ret;
ret = ioprio_check_cap(ioprio);
if (ret)
return ret;
ret = -ESRCH;
ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-11-15 09:20:52 +00:00
rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = set_task_ioprio(p, ioprio);
break;
case IOPRIO_WHO_PGRP:
if (!who)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
ret = set_task_ioprio(p, ioprio);
if (ret) {
read_unlock(&tasklist_lock);
goto out;
}
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
read_unlock(&tasklist_lock);
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
if (!uid_valid(uid))
break;
if (!who)
user = current_user();
else
user = find_user(uid);
if (!user)
break;
for_each_process_thread(g, p) {
2015-11-07 00:32:48 +00:00
if (!uid_eq(task_uid(p), uid) ||
!task_pid_vnr(p))
continue;
ret = set_task_ioprio(p, ioprio);
if (ret)
goto free_uid;
}
free_uid:
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
out:
ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-11-15 09:20:52 +00:00
rcu_read_unlock();
return ret;
}
/*
* If the task has set an I/O priority, use that. Otherwise, return
* the default I/O priority.
*
* Expected to be called for current task or with task_lock() held to keep
* io_context stable.
*/
int __get_task_ioprio(struct task_struct *p)
{
struct io_context *ioc = p->io_context;
int prio;
if (p != current)
lockdep_assert_held(&p->alloc_lock);
if (ioc)
prio = ioc->ioprio;
else
prio = IOPRIO_DEFAULT;
if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p),
task_nice_ioprio(p));
return prio;
}
EXPORT_SYMBOL_GPL(__get_task_ioprio);
static int get_task_ioprio(struct task_struct *p)
{
int ret;
ret = security_task_getioprio(p);
if (ret)
goto out;
task_lock(p);
ret = __get_task_ioprio(p);
task_unlock(p);
out:
return ret;
}
/*
* Return raw IO priority value as set by userspace. We use this for
* ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
* also so that userspace can distinguish unset IO priority (which just gets
* overriden based on task's nice value) from IO priority set to some value.
*/
static int get_task_raw_ioprio(struct task_struct *p)
{
int ret;
ret = security_task_getioprio(p);
if (ret)
goto out;
block: fix use-after-free in sys_ioprio_get() get_task_ioprio() accesses the task->io_context without holding the task lock and thus can race with exit_io_context(), leading to a use-after-free. The reproducer below hits this within a few seconds on my 4-core QEMU VM: #define _GNU_SOURCE #include <assert.h> #include <unistd.h> #include <sys/syscall.h> #include <sys/wait.h> int main(int argc, char **argv) { pid_t pid, child; long nproc, i; /* ioprio_set(IOPRIO_WHO_PROCESS, 0, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0)); */ syscall(SYS_ioprio_set, 1, 0, 0x6000); nproc = sysconf(_SC_NPROCESSORS_ONLN); for (i = 0; i < nproc; i++) { pid = fork(); assert(pid != -1); if (pid == 0) { for (;;) { pid = fork(); assert(pid != -1); if (pid == 0) { _exit(0); } else { child = wait(NULL); assert(child == pid); } } } pid = fork(); assert(pid != -1); if (pid == 0) { for (;;) { /* ioprio_get(IOPRIO_WHO_PGRP, 0); */ syscall(SYS_ioprio_get, 2, 0); } } } for (;;) { /* ioprio_get(IOPRIO_WHO_PGRP, 0); */ syscall(SYS_ioprio_get, 2, 0); } return 0; } This gets us KASAN dumps like this: [ 35.526914] ================================================================== [ 35.530009] BUG: KASAN: out-of-bounds in get_task_ioprio+0x7b/0x90 at addr ffff880066f34e6c [ 35.530009] Read of size 2 by task ioprio-gpf/363 [ 35.530009] ============================================================================= [ 35.530009] BUG blkdev_ioc (Not tainted): kasan: bad access detected [ 35.530009] ----------------------------------------------------------------------------- [ 35.530009] Disabling lock debugging due to kernel taint [ 35.530009] INFO: Allocated in create_task_io_context+0x2b/0x370 age=0 cpu=0 pid=360 [ 35.530009] ___slab_alloc+0x55d/0x5a0 [ 35.530009] __slab_alloc.isra.20+0x2b/0x40 [ 35.530009] kmem_cache_alloc_node+0x84/0x200 [ 35.530009] create_task_io_context+0x2b/0x370 [ 35.530009] get_task_io_context+0x92/0xb0 [ 35.530009] copy_process.part.8+0x5029/0x5660 [ 35.530009] _do_fork+0x155/0x7e0 [ 35.530009] SyS_clone+0x19/0x20 [ 35.530009] do_syscall_64+0x195/0x3a0 [ 35.530009] return_from_SYSCALL_64+0x0/0x6a [ 35.530009] INFO: Freed in put_io_context+0xe7/0x120 age=0 cpu=0 pid=1060 [ 35.530009] __slab_free+0x27b/0x3d0 [ 35.530009] kmem_cache_free+0x1fb/0x220 [ 35.530009] put_io_context+0xe7/0x120 [ 35.530009] put_io_context_active+0x238/0x380 [ 35.530009] exit_io_context+0x66/0x80 [ 35.530009] do_exit+0x158e/0x2b90 [ 35.530009] do_group_exit+0xe5/0x2b0 [ 35.530009] SyS_exit_group+0x1d/0x20 [ 35.530009] entry_SYSCALL_64_fastpath+0x1a/0xa4 [ 35.530009] INFO: Slab 0xffffea00019bcd00 objects=20 used=4 fp=0xffff880066f34ff0 flags=0x1fffe0000004080 [ 35.530009] INFO: Object 0xffff880066f34e58 @offset=3672 fp=0x0000000000000001 [ 35.530009] ================================================================== Fix it by grabbing the task lock while we poke at the io_context. Cc: stable@vger.kernel.org Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-07-01 07:39:35 +00:00
task_lock(p);
if (p->io_context)
ret = p->io_context->ioprio;
else
ret = IOPRIO_DEFAULT;
block: fix use-after-free in sys_ioprio_get() get_task_ioprio() accesses the task->io_context without holding the task lock and thus can race with exit_io_context(), leading to a use-after-free. The reproducer below hits this within a few seconds on my 4-core QEMU VM: #define _GNU_SOURCE #include <assert.h> #include <unistd.h> #include <sys/syscall.h> #include <sys/wait.h> int main(int argc, char **argv) { pid_t pid, child; long nproc, i; /* ioprio_set(IOPRIO_WHO_PROCESS, 0, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0)); */ syscall(SYS_ioprio_set, 1, 0, 0x6000); nproc = sysconf(_SC_NPROCESSORS_ONLN); for (i = 0; i < nproc; i++) { pid = fork(); assert(pid != -1); if (pid == 0) { for (;;) { pid = fork(); assert(pid != -1); if (pid == 0) { _exit(0); } else { child = wait(NULL); assert(child == pid); } } } pid = fork(); assert(pid != -1); if (pid == 0) { for (;;) { /* ioprio_get(IOPRIO_WHO_PGRP, 0); */ syscall(SYS_ioprio_get, 2, 0); } } } for (;;) { /* ioprio_get(IOPRIO_WHO_PGRP, 0); */ syscall(SYS_ioprio_get, 2, 0); } return 0; } This gets us KASAN dumps like this: [ 35.526914] ================================================================== [ 35.530009] BUG: KASAN: out-of-bounds in get_task_ioprio+0x7b/0x90 at addr ffff880066f34e6c [ 35.530009] Read of size 2 by task ioprio-gpf/363 [ 35.530009] ============================================================================= [ 35.530009] BUG blkdev_ioc (Not tainted): kasan: bad access detected [ 35.530009] ----------------------------------------------------------------------------- [ 35.530009] Disabling lock debugging due to kernel taint [ 35.530009] INFO: Allocated in create_task_io_context+0x2b/0x370 age=0 cpu=0 pid=360 [ 35.530009] ___slab_alloc+0x55d/0x5a0 [ 35.530009] __slab_alloc.isra.20+0x2b/0x40 [ 35.530009] kmem_cache_alloc_node+0x84/0x200 [ 35.530009] create_task_io_context+0x2b/0x370 [ 35.530009] get_task_io_context+0x92/0xb0 [ 35.530009] copy_process.part.8+0x5029/0x5660 [ 35.530009] _do_fork+0x155/0x7e0 [ 35.530009] SyS_clone+0x19/0x20 [ 35.530009] do_syscall_64+0x195/0x3a0 [ 35.530009] return_from_SYSCALL_64+0x0/0x6a [ 35.530009] INFO: Freed in put_io_context+0xe7/0x120 age=0 cpu=0 pid=1060 [ 35.530009] __slab_free+0x27b/0x3d0 [ 35.530009] kmem_cache_free+0x1fb/0x220 [ 35.530009] put_io_context+0xe7/0x120 [ 35.530009] put_io_context_active+0x238/0x380 [ 35.530009] exit_io_context+0x66/0x80 [ 35.530009] do_exit+0x158e/0x2b90 [ 35.530009] do_group_exit+0xe5/0x2b0 [ 35.530009] SyS_exit_group+0x1d/0x20 [ 35.530009] entry_SYSCALL_64_fastpath+0x1a/0xa4 [ 35.530009] INFO: Slab 0xffffea00019bcd00 objects=20 used=4 fp=0xffff880066f34ff0 flags=0x1fffe0000004080 [ 35.530009] INFO: Object 0xffff880066f34e58 @offset=3672 fp=0x0000000000000001 [ 35.530009] ================================================================== Fix it by grabbing the task lock while we poke at the io_context. Cc: stable@vger.kernel.org Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-07-01 07:39:35 +00:00
task_unlock(p);
out:
return ret;
}
static int ioprio_best(unsigned short aprio, unsigned short bprio)
{
return min(aprio, bprio);
}
SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
{
struct task_struct *g, *p;
struct user_struct *user;
struct pid *pgrp;
kuid_t uid;
int ret = -ESRCH;
int tmpio;
ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-11-15 09:20:52 +00:00
rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = get_task_raw_ioprio(p);
break;
case IOPRIO_WHO_PGRP:
if (!who)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
tmpio = get_task_ioprio(p);
if (tmpio < 0)
continue;
if (ret == -ESRCH)
ret = tmpio;
else
ret = ioprio_best(ret, tmpio);
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
read_unlock(&tasklist_lock);
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
if (!who)
user = current_user();
else
user = find_user(uid);
if (!user)
break;
for_each_process_thread(g, p) {
2015-11-07 00:32:48 +00:00
if (!uid_eq(task_uid(p), user->uid) ||
!task_pid_vnr(p))
continue;
tmpio = get_task_ioprio(p);
if (tmpio < 0)
continue;
if (ret == -ESRCH)
ret = tmpio;
else
ret = ioprio_best(ret, tmpio);
}
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-11-15 09:20:52 +00:00
rcu_read_unlock();
return ret;
}