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io_uring: check sqring and iopoll_list before shedule 

do this to avoid race below:

         userspace                         kernel

                               |  check sqring and iopoll_list
submit sqe                     |
check IORING_SQ_NEED_WAKEUP    |
(which is not set)    |        |
                               |  set IORING_SQ_NEED_WAKEUP
wait cqe                       |  schedule(never wakeup again)

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/1619018351-75883-1-git-send-email-haoxu@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hao Xu 2021-04-21 23:19:11 +08:00 committed by Jens Axboe
parent f2a48dd09b
commit 724cb4f9ec
1 changed files with 19 additions and 17 deletions
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36
fs/io_uring.c
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@ -6839,27 +6839,29 @@ static int io_sq_thread(void *data)
continue;
}
needs_sched = true;
prepare_to_wait(&sqd->wait, &wait, TASK_INTERRUPTIBLE);
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
if ((ctx->flags & IORING_SETUP_IOPOLL) &&
!list_empty_careful(&ctx->iopoll_list)) {
needs_sched = false;
break;
}
if (io_sqring_entries(ctx)) {
needs_sched = false;
break;
}
}
if (needs_sched && !test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state)) {
if (!test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state)) {
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
io_ring_set_wakeup_flag(ctx);
mutex_unlock(&sqd->lock);
schedule();
mutex_lock(&sqd->lock);
needs_sched = true;
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
if ((ctx->flags & IORING_SETUP_IOPOLL) &&
!list_empty_careful(&ctx->iopoll_list)) {
needs_sched = false;
break;
}
if (io_sqring_entries(ctx)) {
needs_sched = false;
break;
}
}
if (needs_sched) {
mutex_unlock(&sqd->lock);
schedule();
mutex_lock(&sqd->lock);
}
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
io_ring_clear_wakeup_flag(ctx);
}