linux/io_uring/poll.c
Lin Ma 12ad3d2d6c io_uring/poll: fix poll_refs race with cancelation
There is an interesting race condition of poll_refs which could result
in a NULL pointer dereference. The crash trace is like:

KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 30781 Comm: syz-executor.2 Not tainted 6.0.0-g493ffd6605b2 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:io_poll_remove_entry io_uring/poll.c:154 [inline]
RIP: 0010:io_poll_remove_entries+0x171/0x5b4 io_uring/poll.c:190
Code: ...
RSP: 0018:ffff88810dfefba0 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000040000
RDX: ffffc900030c4000 RSI: 000000000003ffff RDI: 0000000000040000
RBP: 0000000000000008 R08: ffffffff9764d3dd R09: fffffbfff3836781
R10: fffffbfff3836781 R11: 0000000000000000 R12: 1ffff11003422d60
R13: ffff88801a116b04 R14: ffff88801a116ac0 R15: dffffc0000000000
FS:  00007f9c07497700(0000) GS:ffff88811a600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffb5c00ea98 CR3: 0000000105680005 CR4: 0000000000770ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 <TASK>
 io_apoll_task_func+0x3f/0xa0 io_uring/poll.c:299
 handle_tw_list io_uring/io_uring.c:1037 [inline]
 tctx_task_work+0x37e/0x4f0 io_uring/io_uring.c:1090
 task_work_run+0x13a/0x1b0 kernel/task_work.c:177
 get_signal+0x2402/0x25a0 kernel/signal.c:2635
 arch_do_signal_or_restart+0x3b/0x660 arch/x86/kernel/signal.c:869
 exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
 exit_to_user_mode_prepare+0xc2/0x160 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
 syscall_exit_to_user_mode+0x58/0x160 kernel/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The root cause for this is a tiny overlooking in
io_poll_check_events() when cocurrently run with poll cancel routine
io_poll_cancel_req().

The interleaving to trigger use-after-free:

CPU0                                       |  CPU1
                                           |
io_apoll_task_func()                       |  io_poll_cancel_req()
 io_poll_check_events()                    |
  // do while first loop                   |
  v = atomic_read(...)                     |
  // v = poll_refs = 1                     |
  ...                                      |  io_poll_mark_cancelled()
                                           |   atomic_or()
                                           |   // poll_refs =
IO_POLL_CANCEL_FLAG | 1
                                           |
  atomic_sub_return(...)                   |
  // poll_refs = IO_POLL_CANCEL_FLAG       |
  // loop continue                         |
                                           |
                                           |  io_poll_execute()
                                           |   io_poll_get_ownership()
                                           |   // poll_refs =
IO_POLL_CANCEL_FLAG | 1
                                           |   // gets the ownership
  v = atomic_read(...)                     |
  // poll_refs not change                  |
                                           |
  if (v & IO_POLL_CANCEL_FLAG)             |
   return -ECANCELED;                      |
  // io_poll_check_events return           |
  // will go into                          |
  // io_req_complete_failed() free req     |
                                           |
                                           |  io_apoll_task_func()
                                           |  // also go into
io_req_complete_failed()

And the interleaving to trigger the kernel WARNING:

CPU0                                       |  CPU1
                                           |
io_apoll_task_func()                       |  io_poll_cancel_req()
 io_poll_check_events()                    |
  // do while first loop                   |
  v = atomic_read(...)                     |
  // v = poll_refs = 1                     |
  ...                                      |  io_poll_mark_cancelled()
                                           |   atomic_or()
                                           |   // poll_refs =
IO_POLL_CANCEL_FLAG | 1
                                           |
  atomic_sub_return(...)                   |
  // poll_refs = IO_POLL_CANCEL_FLAG       |
  // loop continue                         |
                                           |
  v = atomic_read(...)                     |
  // v = IO_POLL_CANCEL_FLAG               |
                                           |  io_poll_execute()
                                           |   io_poll_get_ownership()
                                           |   // poll_refs =
IO_POLL_CANCEL_FLAG | 1
                                           |   // gets the ownership
                                           |
  WARN_ON_ONCE(!(v & IO_POLL_REF_MASK)))   |
  // v & IO_POLL_REF_MASK = 0 WARN         |
                                           |
                                           |  io_apoll_task_func()
                                           |  // also go into
io_req_complete_failed()

By looking up the source code and communicating with Pavel, the
implementation of this atomic poll refs should continue the loop of
io_poll_check_events() just to avoid somewhere else to grab the
ownership. Therefore, this patch simply adds another AND operation to
make sure the loop will stop if it finds the poll_refs is exactly equal
to IO_POLL_CANCEL_FLAG. Since io_poll_cancel_req() grabs ownership and
will finally make its way to io_req_complete_failed(), the req will
be reclaimed as expected.

Fixes: aa43477b04 ("io_uring: poll rework")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: tweak description and code style]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-11-25 07:17:33 -07:00

1018 lines
27 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/hashtable.h>
#include <linux/io_uring.h>
#include <trace/events/io_uring.h>
#include <uapi/linux/io_uring.h>
#include "io_uring.h"
#include "refs.h"
#include "opdef.h"
#include "kbuf.h"
#include "poll.h"
#include "cancel.h"
struct io_poll_update {
struct file *file;
u64 old_user_data;
u64 new_user_data;
__poll_t events;
bool update_events;
bool update_user_data;
};
struct io_poll_table {
struct poll_table_struct pt;
struct io_kiocb *req;
int nr_entries;
int error;
bool owning;
/* output value, set only if arm poll returns >0 */
__poll_t result_mask;
};
#define IO_POLL_CANCEL_FLAG BIT(31)
#define IO_POLL_RETRY_FLAG BIT(30)
#define IO_POLL_REF_MASK GENMASK(29, 0)
/*
* We usually have 1-2 refs taken, 128 is more than enough and we want to
* maximise the margin between this amount and the moment when it overflows.
*/
#define IO_POLL_REF_BIAS 128
#define IO_WQE_F_DOUBLE 1
static inline struct io_kiocb *wqe_to_req(struct wait_queue_entry *wqe)
{
unsigned long priv = (unsigned long)wqe->private;
return (struct io_kiocb *)(priv & ~IO_WQE_F_DOUBLE);
}
static inline bool wqe_is_double(struct wait_queue_entry *wqe)
{
unsigned long priv = (unsigned long)wqe->private;
return priv & IO_WQE_F_DOUBLE;
}
static bool io_poll_get_ownership_slowpath(struct io_kiocb *req)
{
int v;
/*
* poll_refs are already elevated and we don't have much hope for
* grabbing the ownership. Instead of incrementing set a retry flag
* to notify the loop that there might have been some change.
*/
v = atomic_fetch_or(IO_POLL_RETRY_FLAG, &req->poll_refs);
if (v & IO_POLL_REF_MASK)
return false;
return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
}
/*
* If refs part of ->poll_refs (see IO_POLL_REF_MASK) is 0, it's free. We can
* bump it and acquire ownership. It's disallowed to modify requests while not
* owning it, that prevents from races for enqueueing task_work's and b/w
* arming poll and wakeups.
*/
static inline bool io_poll_get_ownership(struct io_kiocb *req)
{
if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))
return io_poll_get_ownership_slowpath(req);
return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
}
static void io_poll_mark_cancelled(struct io_kiocb *req)
{
atomic_or(IO_POLL_CANCEL_FLAG, &req->poll_refs);
}
static struct io_poll *io_poll_get_double(struct io_kiocb *req)
{
/* pure poll stashes this in ->async_data, poll driven retry elsewhere */
if (req->opcode == IORING_OP_POLL_ADD)
return req->async_data;
return req->apoll->double_poll;
}
static struct io_poll *io_poll_get_single(struct io_kiocb *req)
{
if (req->opcode == IORING_OP_POLL_ADD)
return io_kiocb_to_cmd(req, struct io_poll);
return &req->apoll->poll;
}
static void io_poll_req_insert(struct io_kiocb *req)
{
struct io_hash_table *table = &req->ctx->cancel_table;
u32 index = hash_long(req->cqe.user_data, table->hash_bits);
struct io_hash_bucket *hb = &table->hbs[index];
spin_lock(&hb->lock);
hlist_add_head(&req->hash_node, &hb->list);
spin_unlock(&hb->lock);
}
static void io_poll_req_delete(struct io_kiocb *req, struct io_ring_ctx *ctx)
{
struct io_hash_table *table = &req->ctx->cancel_table;
u32 index = hash_long(req->cqe.user_data, table->hash_bits);
spinlock_t *lock = &table->hbs[index].lock;
spin_lock(lock);
hash_del(&req->hash_node);
spin_unlock(lock);
}
static void io_poll_req_insert_locked(struct io_kiocb *req)
{
struct io_hash_table *table = &req->ctx->cancel_table_locked;
u32 index = hash_long(req->cqe.user_data, table->hash_bits);
lockdep_assert_held(&req->ctx->uring_lock);
hlist_add_head(&req->hash_node, &table->hbs[index].list);
}
static void io_poll_tw_hash_eject(struct io_kiocb *req, bool *locked)
{
struct io_ring_ctx *ctx = req->ctx;
if (req->flags & REQ_F_HASH_LOCKED) {
/*
* ->cancel_table_locked is protected by ->uring_lock in
* contrast to per bucket spinlocks. Likely, tctx_task_work()
* already grabbed the mutex for us, but there is a chance it
* failed.
*/
io_tw_lock(ctx, locked);
hash_del(&req->hash_node);
req->flags &= ~REQ_F_HASH_LOCKED;
} else {
io_poll_req_delete(req, ctx);
}
}
static void io_init_poll_iocb(struct io_poll *poll, __poll_t events,
wait_queue_func_t wake_func)
{
poll->head = NULL;
#define IO_POLL_UNMASK (EPOLLERR|EPOLLHUP|EPOLLNVAL|EPOLLRDHUP)
/* mask in events that we always want/need */
poll->events = events | IO_POLL_UNMASK;
INIT_LIST_HEAD(&poll->wait.entry);
init_waitqueue_func_entry(&poll->wait, wake_func);
}
static inline void io_poll_remove_entry(struct io_poll *poll)
{
struct wait_queue_head *head = smp_load_acquire(&poll->head);
if (head) {
spin_lock_irq(&head->lock);
list_del_init(&poll->wait.entry);
poll->head = NULL;
spin_unlock_irq(&head->lock);
}
}
static void io_poll_remove_entries(struct io_kiocb *req)
{
/*
* Nothing to do if neither of those flags are set. Avoid dipping
* into the poll/apoll/double cachelines if we can.
*/
if (!(req->flags & (REQ_F_SINGLE_POLL | REQ_F_DOUBLE_POLL)))
return;
/*
* While we hold the waitqueue lock and the waitqueue is nonempty,
* wake_up_pollfree() will wait for us. However, taking the waitqueue
* lock in the first place can race with the waitqueue being freed.
*
* We solve this as eventpoll does: by taking advantage of the fact that
* all users of wake_up_pollfree() will RCU-delay the actual free. If
* we enter rcu_read_lock() and see that the pointer to the queue is
* non-NULL, we can then lock it without the memory being freed out from
* under us.
*
* Keep holding rcu_read_lock() as long as we hold the queue lock, in
* case the caller deletes the entry from the queue, leaving it empty.
* In that case, only RCU prevents the queue memory from being freed.
*/
rcu_read_lock();
if (req->flags & REQ_F_SINGLE_POLL)
io_poll_remove_entry(io_poll_get_single(req));
if (req->flags & REQ_F_DOUBLE_POLL)
io_poll_remove_entry(io_poll_get_double(req));
rcu_read_unlock();
}
enum {
IOU_POLL_DONE = 0,
IOU_POLL_NO_ACTION = 1,
IOU_POLL_REMOVE_POLL_USE_RES = 2,
};
/*
* All poll tw should go through this. Checks for poll events, manages
* references, does rewait, etc.
*
* Returns a negative error on failure. IOU_POLL_NO_ACTION when no action require,
* which is either spurious wakeup or multishot CQE is served.
* IOU_POLL_DONE when it's done with the request, then the mask is stored in req->cqe.res.
* IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot poll and that the result
* is stored in req->cqe.
*/
static int io_poll_check_events(struct io_kiocb *req, bool *locked)
{
struct io_ring_ctx *ctx = req->ctx;
int v, ret;
/* req->task == current here, checking PF_EXITING is safe */
if (unlikely(req->task->flags & PF_EXITING))
return -ECANCELED;
do {
v = atomic_read(&req->poll_refs);
/* tw handler should be the owner, and so have some references */
if (WARN_ON_ONCE(!(v & IO_POLL_REF_MASK)))
return IOU_POLL_DONE;
if (v & IO_POLL_CANCEL_FLAG)
return -ECANCELED;
/*
* cqe.res contains only events of the first wake up
* and all others are be lost. Redo vfs_poll() to get
* up to date state.
*/
if ((v & IO_POLL_REF_MASK) != 1)
req->cqe.res = 0;
if (v & IO_POLL_RETRY_FLAG) {
req->cqe.res = 0;
/*
* We won't find new events that came in between
* vfs_poll and the ref put unless we clear the flag
* in advance.
*/
atomic_andnot(IO_POLL_RETRY_FLAG, &req->poll_refs);
v &= ~IO_POLL_RETRY_FLAG;
}
/* the mask was stashed in __io_poll_execute */
if (!req->cqe.res) {
struct poll_table_struct pt = { ._key = req->apoll_events };
req->cqe.res = vfs_poll(req->file, &pt) & req->apoll_events;
}
if ((unlikely(!req->cqe.res)))
continue;
if (req->apoll_events & EPOLLONESHOT)
return IOU_POLL_DONE;
if (io_is_uring_fops(req->file))
return IOU_POLL_DONE;
/* multishot, just fill a CQE and proceed */
if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
__poll_t mask = mangle_poll(req->cqe.res &
req->apoll_events);
if (!io_post_aux_cqe(ctx, req->cqe.user_data,
mask, IORING_CQE_F_MORE, false)) {
io_req_set_res(req, mask, 0);
return IOU_POLL_REMOVE_POLL_USE_RES;
}
} else {
ret = io_poll_issue(req, locked);
if (ret == IOU_STOP_MULTISHOT)
return IOU_POLL_REMOVE_POLL_USE_RES;
if (ret < 0)
return ret;
}
/* force the next iteration to vfs_poll() */
req->cqe.res = 0;
/*
* Release all references, retry if someone tried to restart
* task_work while we were executing it.
*/
} while (atomic_sub_return(v & IO_POLL_REF_MASK, &req->poll_refs) &
IO_POLL_REF_MASK);
return IOU_POLL_NO_ACTION;
}
static void io_poll_task_func(struct io_kiocb *req, bool *locked)
{
int ret;
ret = io_poll_check_events(req, locked);
if (ret == IOU_POLL_NO_ACTION)
return;
if (ret == IOU_POLL_DONE) {
struct io_poll *poll = io_kiocb_to_cmd(req, struct io_poll);
req->cqe.res = mangle_poll(req->cqe.res & poll->events);
} else if (ret != IOU_POLL_REMOVE_POLL_USE_RES) {
req->cqe.res = ret;
req_set_fail(req);
}
io_poll_remove_entries(req);
io_poll_tw_hash_eject(req, locked);
io_req_set_res(req, req->cqe.res, 0);
io_req_task_complete(req, locked);
}
static void io_apoll_task_func(struct io_kiocb *req, bool *locked)
{
int ret;
ret = io_poll_check_events(req, locked);
if (ret == IOU_POLL_NO_ACTION)
return;
io_poll_remove_entries(req);
io_poll_tw_hash_eject(req, locked);
if (ret == IOU_POLL_REMOVE_POLL_USE_RES)
io_req_complete_post(req);
else if (ret == IOU_POLL_DONE)
io_req_task_submit(req, locked);
else
io_req_complete_failed(req, ret);
}
static void __io_poll_execute(struct io_kiocb *req, int mask)
{
io_req_set_res(req, mask, 0);
/*
* This is useful for poll that is armed on behalf of another
* request, and where the wakeup path could be on a different
* CPU. We want to avoid pulling in req->apoll->events for that
* case.
*/
if (req->opcode == IORING_OP_POLL_ADD)
req->io_task_work.func = io_poll_task_func;
else
req->io_task_work.func = io_apoll_task_func;
trace_io_uring_task_add(req, mask);
io_req_task_work_add(req);
}
static inline void io_poll_execute(struct io_kiocb *req, int res)
{
if (io_poll_get_ownership(req))
__io_poll_execute(req, res);
}
static void io_poll_cancel_req(struct io_kiocb *req)
{
io_poll_mark_cancelled(req);
/* kick tw, which should complete the request */
io_poll_execute(req, 0);
}
#define IO_ASYNC_POLL_COMMON (EPOLLONESHOT | EPOLLPRI)
static __cold int io_pollfree_wake(struct io_kiocb *req, struct io_poll *poll)
{
io_poll_mark_cancelled(req);
/* we have to kick tw in case it's not already */
io_poll_execute(req, 0);
/*
* If the waitqueue is being freed early but someone is already
* holds ownership over it, we have to tear down the request as
* best we can. That means immediately removing the request from
* its waitqueue and preventing all further accesses to the
* waitqueue via the request.
*/
list_del_init(&poll->wait.entry);
/*
* Careful: this *must* be the last step, since as soon
* as req->head is NULL'ed out, the request can be
* completed and freed, since aio_poll_complete_work()
* will no longer need to take the waitqueue lock.
*/
smp_store_release(&poll->head, NULL);
return 1;
}
static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
void *key)
{
struct io_kiocb *req = wqe_to_req(wait);
struct io_poll *poll = container_of(wait, struct io_poll, wait);
__poll_t mask = key_to_poll(key);
if (unlikely(mask & POLLFREE))
return io_pollfree_wake(req, poll);
/* for instances that support it check for an event match first */
if (mask && !(mask & (poll->events & ~IO_ASYNC_POLL_COMMON)))
return 0;
if (io_poll_get_ownership(req)) {
/* optional, saves extra locking for removal in tw handler */
if (mask && poll->events & EPOLLONESHOT) {
list_del_init(&poll->wait.entry);
poll->head = NULL;
if (wqe_is_double(wait))
req->flags &= ~REQ_F_DOUBLE_POLL;
else
req->flags &= ~REQ_F_SINGLE_POLL;
}
__io_poll_execute(req, mask);
}
return 1;
}
/* fails only when polling is already completing by the first entry */
static bool io_poll_double_prepare(struct io_kiocb *req)
{
struct wait_queue_head *head;
struct io_poll *poll = io_poll_get_single(req);
/* head is RCU protected, see io_poll_remove_entries() comments */
rcu_read_lock();
head = smp_load_acquire(&poll->head);
/*
* poll arm might not hold ownership and so race for req->flags with
* io_poll_wake(). There is only one poll entry queued, serialise with
* it by taking its head lock. As we're still arming the tw hanlder
* is not going to be run, so there are no races with it.
*/
if (head) {
spin_lock_irq(&head->lock);
req->flags |= REQ_F_DOUBLE_POLL;
if (req->opcode == IORING_OP_POLL_ADD)
req->flags |= REQ_F_ASYNC_DATA;
spin_unlock_irq(&head->lock);
}
rcu_read_unlock();
return !!head;
}
static void __io_queue_proc(struct io_poll *poll, struct io_poll_table *pt,
struct wait_queue_head *head,
struct io_poll **poll_ptr)
{
struct io_kiocb *req = pt->req;
unsigned long wqe_private = (unsigned long) req;
/*
* The file being polled uses multiple waitqueues for poll handling
* (e.g. one for read, one for write). Setup a separate io_poll
* if this happens.
*/
if (unlikely(pt->nr_entries)) {
struct io_poll *first = poll;
/* double add on the same waitqueue head, ignore */
if (first->head == head)
return;
/* already have a 2nd entry, fail a third attempt */
if (*poll_ptr) {
if ((*poll_ptr)->head == head)
return;
pt->error = -EINVAL;
return;
}
poll = kmalloc(sizeof(*poll), GFP_ATOMIC);
if (!poll) {
pt->error = -ENOMEM;
return;
}
/* mark as double wq entry */
wqe_private |= IO_WQE_F_DOUBLE;
io_init_poll_iocb(poll, first->events, first->wait.func);
if (!io_poll_double_prepare(req)) {
/* the request is completing, just back off */
kfree(poll);
return;
}
*poll_ptr = poll;
} else {
/* fine to modify, there is no poll queued to race with us */
req->flags |= REQ_F_SINGLE_POLL;
}
pt->nr_entries++;
poll->head = head;
poll->wait.private = (void *) wqe_private;
if (poll->events & EPOLLEXCLUSIVE)
add_wait_queue_exclusive(head, &poll->wait);
else
add_wait_queue(head, &poll->wait);
}
static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
struct poll_table_struct *p)
{
struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
struct io_poll *poll = io_kiocb_to_cmd(pt->req, struct io_poll);
__io_queue_proc(poll, pt, head,
(struct io_poll **) &pt->req->async_data);
}
static bool io_poll_can_finish_inline(struct io_kiocb *req,
struct io_poll_table *pt)
{
return pt->owning || io_poll_get_ownership(req);
}
/*
* Returns 0 when it's handed over for polling. The caller owns the requests if
* it returns non-zero, but otherwise should not touch it. Negative values
* contain an error code. When the result is >0, the polling has completed
* inline and ipt.result_mask is set to the mask.
*/
static int __io_arm_poll_handler(struct io_kiocb *req,
struct io_poll *poll,
struct io_poll_table *ipt, __poll_t mask,
unsigned issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
INIT_HLIST_NODE(&req->hash_node);
req->work.cancel_seq = atomic_read(&ctx->cancel_seq);
io_init_poll_iocb(poll, mask, io_poll_wake);
poll->file = req->file;
req->apoll_events = poll->events;
ipt->pt._key = mask;
ipt->req = req;
ipt->error = 0;
ipt->nr_entries = 0;
/*
* Polling is either completed here or via task_work, so if we're in the
* task context we're naturally serialised with tw by merit of running
* the same task. When it's io-wq, take the ownership to prevent tw
* from running. However, when we're in the task context, skip taking
* it as an optimisation.
*
* Note: even though the request won't be completed/freed, without
* ownership we still can race with io_poll_wake().
* io_poll_can_finish_inline() tries to deal with that.
*/
ipt->owning = issue_flags & IO_URING_F_UNLOCKED;
atomic_set(&req->poll_refs, (int)ipt->owning);
/* io-wq doesn't hold uring_lock */
if (issue_flags & IO_URING_F_UNLOCKED)
req->flags &= ~REQ_F_HASH_LOCKED;
mask = vfs_poll(req->file, &ipt->pt) & poll->events;
if (unlikely(ipt->error || !ipt->nr_entries)) {
io_poll_remove_entries(req);
if (!io_poll_can_finish_inline(req, ipt)) {
io_poll_mark_cancelled(req);
return 0;
} else if (mask && (poll->events & EPOLLET)) {
ipt->result_mask = mask;
return 1;
}
return ipt->error ?: -EINVAL;
}
if (mask &&
((poll->events & (EPOLLET|EPOLLONESHOT)) == (EPOLLET|EPOLLONESHOT))) {
if (!io_poll_can_finish_inline(req, ipt))
return 0;
io_poll_remove_entries(req);
ipt->result_mask = mask;
/* no one else has access to the req, forget about the ref */
return 1;
}
if (req->flags & REQ_F_HASH_LOCKED)
io_poll_req_insert_locked(req);
else
io_poll_req_insert(req);
if (mask && (poll->events & EPOLLET) &&
io_poll_can_finish_inline(req, ipt)) {
__io_poll_execute(req, mask);
return 0;
}
if (ipt->owning) {
/*
* Try to release ownership. If we see a change of state, e.g.
* poll was waken up, queue up a tw, it'll deal with it.
*/
if (atomic_cmpxchg(&req->poll_refs, 1, 0) != 1)
__io_poll_execute(req, 0);
}
return 0;
}
static void io_async_queue_proc(struct file *file, struct wait_queue_head *head,
struct poll_table_struct *p)
{
struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
struct async_poll *apoll = pt->req->apoll;
__io_queue_proc(&apoll->poll, pt, head, &apoll->double_poll);
}
static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req,
unsigned issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_cache_entry *entry;
struct async_poll *apoll;
if (req->flags & REQ_F_POLLED) {
apoll = req->apoll;
kfree(apoll->double_poll);
} else if (!(issue_flags & IO_URING_F_UNLOCKED) &&
(entry = io_alloc_cache_get(&ctx->apoll_cache)) != NULL) {
apoll = container_of(entry, struct async_poll, cache);
} else {
apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
if (unlikely(!apoll))
return NULL;
}
apoll->double_poll = NULL;
req->apoll = apoll;
return apoll;
}
int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
{
const struct io_op_def *def = &io_op_defs[req->opcode];
struct async_poll *apoll;
struct io_poll_table ipt;
__poll_t mask = POLLPRI | POLLERR | EPOLLET;
int ret;
/*
* apoll requests already grab the mutex to complete in the tw handler,
* so removal from the mutex-backed hash is free, use it by default.
*/
req->flags |= REQ_F_HASH_LOCKED;
if (!def->pollin && !def->pollout)
return IO_APOLL_ABORTED;
if (!file_can_poll(req->file))
return IO_APOLL_ABORTED;
if ((req->flags & (REQ_F_POLLED|REQ_F_PARTIAL_IO)) == REQ_F_POLLED)
return IO_APOLL_ABORTED;
if (!(req->flags & REQ_F_APOLL_MULTISHOT))
mask |= EPOLLONESHOT;
if (def->pollin) {
mask |= EPOLLIN | EPOLLRDNORM;
/* If reading from MSG_ERRQUEUE using recvmsg, ignore POLLIN */
if (req->flags & REQ_F_CLEAR_POLLIN)
mask &= ~EPOLLIN;
} else {
mask |= EPOLLOUT | EPOLLWRNORM;
}
if (def->poll_exclusive)
mask |= EPOLLEXCLUSIVE;
apoll = io_req_alloc_apoll(req, issue_flags);
if (!apoll)
return IO_APOLL_ABORTED;
req->flags |= REQ_F_POLLED;
ipt.pt._qproc = io_async_queue_proc;
io_kbuf_recycle(req, issue_flags);
ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask, issue_flags);
if (ret)
return ret > 0 ? IO_APOLL_READY : IO_APOLL_ABORTED;
trace_io_uring_poll_arm(req, mask, apoll->poll.events);
return IO_APOLL_OK;
}
static __cold bool io_poll_remove_all_table(struct task_struct *tsk,
struct io_hash_table *table,
bool cancel_all)
{
unsigned nr_buckets = 1U << table->hash_bits;
struct hlist_node *tmp;
struct io_kiocb *req;
bool found = false;
int i;
for (i = 0; i < nr_buckets; i++) {
struct io_hash_bucket *hb = &table->hbs[i];
spin_lock(&hb->lock);
hlist_for_each_entry_safe(req, tmp, &hb->list, hash_node) {
if (io_match_task_safe(req, tsk, cancel_all)) {
hlist_del_init(&req->hash_node);
io_poll_cancel_req(req);
found = true;
}
}
spin_unlock(&hb->lock);
}
return found;
}
/*
* Returns true if we found and killed one or more poll requests
*/
__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
bool cancel_all)
__must_hold(&ctx->uring_lock)
{
bool ret;
ret = io_poll_remove_all_table(tsk, &ctx->cancel_table, cancel_all);
ret |= io_poll_remove_all_table(tsk, &ctx->cancel_table_locked, cancel_all);
return ret;
}
static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only,
struct io_cancel_data *cd,
struct io_hash_table *table,
struct io_hash_bucket **out_bucket)
{
struct io_kiocb *req;
u32 index = hash_long(cd->data, table->hash_bits);
struct io_hash_bucket *hb = &table->hbs[index];
*out_bucket = NULL;
spin_lock(&hb->lock);
hlist_for_each_entry(req, &hb->list, hash_node) {
if (cd->data != req->cqe.user_data)
continue;
if (poll_only && req->opcode != IORING_OP_POLL_ADD)
continue;
if (cd->flags & IORING_ASYNC_CANCEL_ALL) {
if (cd->seq == req->work.cancel_seq)
continue;
req->work.cancel_seq = cd->seq;
}
*out_bucket = hb;
return req;
}
spin_unlock(&hb->lock);
return NULL;
}
static struct io_kiocb *io_poll_file_find(struct io_ring_ctx *ctx,
struct io_cancel_data *cd,
struct io_hash_table *table,
struct io_hash_bucket **out_bucket)
{
unsigned nr_buckets = 1U << table->hash_bits;
struct io_kiocb *req;
int i;
*out_bucket = NULL;
for (i = 0; i < nr_buckets; i++) {
struct io_hash_bucket *hb = &table->hbs[i];
spin_lock(&hb->lock);
hlist_for_each_entry(req, &hb->list, hash_node) {
if (!(cd->flags & IORING_ASYNC_CANCEL_ANY) &&
req->file != cd->file)
continue;
if (cd->seq == req->work.cancel_seq)
continue;
req->work.cancel_seq = cd->seq;
*out_bucket = hb;
return req;
}
spin_unlock(&hb->lock);
}
return NULL;
}
static int io_poll_disarm(struct io_kiocb *req)
{
if (!req)
return -ENOENT;
if (!io_poll_get_ownership(req))
return -EALREADY;
io_poll_remove_entries(req);
hash_del(&req->hash_node);
return 0;
}
static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
struct io_hash_table *table)
{
struct io_hash_bucket *bucket;
struct io_kiocb *req;
if (cd->flags & (IORING_ASYNC_CANCEL_FD|IORING_ASYNC_CANCEL_ANY))
req = io_poll_file_find(ctx, cd, table, &bucket);
else
req = io_poll_find(ctx, false, cd, table, &bucket);
if (req)
io_poll_cancel_req(req);
if (bucket)
spin_unlock(&bucket->lock);
return req ? 0 : -ENOENT;
}
int io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
unsigned issue_flags)
{
int ret;
ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table);
if (ret != -ENOENT)
return ret;
io_ring_submit_lock(ctx, issue_flags);
ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table_locked);
io_ring_submit_unlock(ctx, issue_flags);
return ret;
}
static __poll_t io_poll_parse_events(const struct io_uring_sqe *sqe,
unsigned int flags)
{
u32 events;
events = READ_ONCE(sqe->poll32_events);
#ifdef __BIG_ENDIAN
events = swahw32(events);
#endif
if (!(flags & IORING_POLL_ADD_MULTI))
events |= EPOLLONESHOT;
if (!(flags & IORING_POLL_ADD_LEVEL))
events |= EPOLLET;
return demangle_poll(events) |
(events & (EPOLLEXCLUSIVE|EPOLLONESHOT|EPOLLET));
}
int io_poll_remove_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
struct io_poll_update *upd = io_kiocb_to_cmd(req, struct io_poll_update);
u32 flags;
if (sqe->buf_index || sqe->splice_fd_in)
return -EINVAL;
flags = READ_ONCE(sqe->len);
if (flags & ~(IORING_POLL_UPDATE_EVENTS | IORING_POLL_UPDATE_USER_DATA |
IORING_POLL_ADD_MULTI))
return -EINVAL;
/* meaningless without update */
if (flags == IORING_POLL_ADD_MULTI)
return -EINVAL;
upd->old_user_data = READ_ONCE(sqe->addr);
upd->update_events = flags & IORING_POLL_UPDATE_EVENTS;
upd->update_user_data = flags & IORING_POLL_UPDATE_USER_DATA;
upd->new_user_data = READ_ONCE(sqe->off);
if (!upd->update_user_data && upd->new_user_data)
return -EINVAL;
if (upd->update_events)
upd->events = io_poll_parse_events(sqe, flags);
else if (sqe->poll32_events)
return -EINVAL;
return 0;
}
int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
struct io_poll *poll = io_kiocb_to_cmd(req, struct io_poll);
u32 flags;
if (sqe->buf_index || sqe->off || sqe->addr)
return -EINVAL;
flags = READ_ONCE(sqe->len);
if (flags & ~IORING_POLL_ADD_MULTI)
return -EINVAL;
if ((flags & IORING_POLL_ADD_MULTI) && (req->flags & REQ_F_CQE_SKIP))
return -EINVAL;
poll->events = io_poll_parse_events(sqe, flags);
return 0;
}
int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_poll *poll = io_kiocb_to_cmd(req, struct io_poll);
struct io_poll_table ipt;
int ret;
ipt.pt._qproc = io_poll_queue_proc;
/*
* If sqpoll or single issuer, there is no contention for ->uring_lock
* and we'll end up holding it in tw handlers anyway.
*/
if (req->ctx->flags & (IORING_SETUP_SQPOLL|IORING_SETUP_SINGLE_ISSUER))
req->flags |= REQ_F_HASH_LOCKED;
ret = __io_arm_poll_handler(req, poll, &ipt, poll->events, issue_flags);
if (ret > 0) {
io_req_set_res(req, ipt.result_mask, 0);
return IOU_OK;
}
return ret ?: IOU_ISSUE_SKIP_COMPLETE;
}
int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_poll_update *poll_update = io_kiocb_to_cmd(req, struct io_poll_update);
struct io_cancel_data cd = { .data = poll_update->old_user_data, };
struct io_ring_ctx *ctx = req->ctx;
struct io_hash_bucket *bucket;
struct io_kiocb *preq;
int ret2, ret = 0;
bool locked;
preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table, &bucket);
ret2 = io_poll_disarm(preq);
if (bucket)
spin_unlock(&bucket->lock);
if (!ret2)
goto found;
if (ret2 != -ENOENT) {
ret = ret2;
goto out;
}
io_ring_submit_lock(ctx, issue_flags);
preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table_locked, &bucket);
ret2 = io_poll_disarm(preq);
if (bucket)
spin_unlock(&bucket->lock);
io_ring_submit_unlock(ctx, issue_flags);
if (ret2) {
ret = ret2;
goto out;
}
found:
if (WARN_ON_ONCE(preq->opcode != IORING_OP_POLL_ADD)) {
ret = -EFAULT;
goto out;
}
if (poll_update->update_events || poll_update->update_user_data) {
/* only mask one event flags, keep behavior flags */
if (poll_update->update_events) {
struct io_poll *poll = io_kiocb_to_cmd(preq, struct io_poll);
poll->events &= ~0xffff;
poll->events |= poll_update->events & 0xffff;
poll->events |= IO_POLL_UNMASK;
}
if (poll_update->update_user_data)
preq->cqe.user_data = poll_update->new_user_data;
ret2 = io_poll_add(preq, issue_flags);
/* successfully updated, don't complete poll request */
if (!ret2 || ret2 == -EIOCBQUEUED)
goto out;
}
req_set_fail(preq);
io_req_set_res(preq, -ECANCELED, 0);
locked = !(issue_flags & IO_URING_F_UNLOCKED);
io_req_task_complete(preq, &locked);
out:
if (ret < 0) {
req_set_fail(req);
return ret;
}
/* complete update request, we're done with it */
io_req_set_res(req, ret, 0);
return IOU_OK;
}
void io_apoll_cache_free(struct io_cache_entry *entry)
{
kfree(container_of(entry, struct async_poll, cache));
}