Commit 9939a467 authored by Jens Axboe's avatar Jens Axboe Committed by Wen Zhiwei
Browse files

io_uring: check for presence of task_work rather than TIF_NOTIFY_SIGNAL 

stable inclusion
from stable-v6.6.54
commit 4bdf75c2ef3311342d35dae23f439439ec7a6886
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IAZ3K2

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4bdf75c2ef3311342d35dae23f439439ec7a6886



--------------------------------

commit 04beb6e0e08c30c6f845f50afb7d7953603d7a6f upstream.

If some part of the kernel adds task_work that needs executing, in terms
of signaling it'll generally use TWA_SIGNAL or TWA_RESUME. Those two
directly translate to TIF_NOTIFY_SIGNAL or TIF_NOTIFY_RESUME, and can
be used for a variety of use case outside of task_work.

However, io_cqring_wait_schedule() only tests explicitly for
TIF_NOTIFY_SIGNAL. This means it can miss if task_work got added for
the task, but used a different kind of signaling mechanism (or none at
all). Normally this doesn't matter as any task_work will be run once
the task exits to userspace, except if:

1) The ring is setup with DEFER_TASKRUN
2) The local work item may generate normal task_work

For condition 2, this can happen when closing a file and it's the final
put of that file, for example. This can cause stalls where a task is
waiting to make progress inside io_cqring_wait(), but there's nothing else
that will wake it up. Hence change the "should we schedule or loop around"
check to check for the presence of task_work explicitly, rather than just
TIF_NOTIFY_SIGNAL as the mechanism. While in there, also change the
ordering of what type of task_work first in terms of ordering, to both
make it consistent with other task_work runs in io_uring, but also to
better handle the case of defer task_work generating normal task_work,
like in the above example.

Reported-by: default avatarJan Hendrik Farr <kernel@jfarr.cc>
Link: https://github.com/axboe/liburing/issues/1235


Cc: stable@vger.kernel.org
Fixes: 846072f1 ("io_uring: mimimise io_cqring_wait_schedule")
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarWen Zhiwei <wenzhiwei@kylinos.cn>
parent cbf8d7ac

io_uring/io_uring.c

+2 −2
Original line number Diff line number Diff line
@@ -2517,7 +2517,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, 
		return 1;

	if (unlikely(!llist_empty(&ctx->work_llist)))

		return 1;

	if (unlikely(test_thread_flag(TIF_NOTIFY_SIGNAL)))

	if (unlikely(task_work_pending(current)))

		return 1;

	if (unlikely(task_sigpending(current)))

		return -EINTR;
@@ -2613,9 +2613,9 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, 
		 * If we got woken because of task_work being processed, run it

		 * now rather than let the caller do another wait loop.

		 */

		io_run_task_work();

		if (!llist_empty(&ctx->work_llist))

			io_run_local_work(ctx, nr_wait);

		io_run_task_work();



		/*

		 * Non-local task_work will be run on exit to userspace, but