Patch "io_uring: fix io_queue_proc modifying req->flags" has been added to the 6.8-stable tree

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This is a note to let you know that I've just added the patch titled

    io_uring: fix io_queue_proc modifying req->flags

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     io_uring-fix-io_queue_proc-modifying-req-flags.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 78b414c246782d766fadacdf435fcc53d8a6019b
Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
Date:   Thu Mar 7 18:06:32 2024 +0000

    io_uring: fix io_queue_proc modifying req->flags
    
    [ Upstream commit 1a8ec63b2b6c91caec87d4e132b1f71b5df342be ]
    
    With multiple poll entries __io_queue_proc() might be running in
    parallel with poll handlers and possibly task_work, we should not be
    carelessly modifying req->flags there. io_poll_double_prepare() handles
    a similar case with locking but it's much easier to move it into
    __io_arm_poll_handler().
    
    Cc: stable@xxxxxxxxxxxxxxx
    Fixes: 595e52284d24a ("io_uring/poll: don't enable lazy wake for POLLEXCLUSIVE")
    Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
    Link: https://lore.kernel.org/r/455cc49e38cf32026fa1b49670be8c162c2cb583.1709834755.git.asml.silence@xxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/io_uring/poll.c b/io_uring/poll.c
index 58b7556f621eb..c6f4789623cb2 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -539,14 +539,6 @@ static void __io_queue_proc(struct io_poll *poll, struct io_poll_table *pt,
 	poll->wait.private = (void *) wqe_private;
 
 	if (poll->events & EPOLLEXCLUSIVE) {
-		/*
-		 * Exclusive waits may only wake a limited amount of entries
-		 * rather than all of them, this may interfere with lazy
-		 * wake if someone does wait(events > 1). Ensure we don't do
-		 * lazy wake for those, as we need to process each one as they
-		 * come in.
-		 */
-		req->flags |= REQ_F_POLL_NO_LAZY;
 		add_wait_queue_exclusive(head, &poll->wait);
 	} else {
 		add_wait_queue(head, &poll->wait);
@@ -618,6 +610,17 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
 	if (issue_flags & IO_URING_F_UNLOCKED)
 		req->flags &= ~REQ_F_HASH_LOCKED;
 
+
+	/*
+	 * Exclusive waits may only wake a limited amount of entries
+	 * rather than all of them, this may interfere with lazy
+	 * wake if someone does wait(events > 1). Ensure we don't do
+	 * lazy wake for those, as we need to process each one as they
+	 * come in.
+	 */
+	if (poll->events & EPOLLEXCLUSIVE)
+		req->flags |= REQ_F_POLL_NO_LAZY;
+
 	mask = vfs_poll(req->file, &ipt->pt) & poll->events;
 
 	if (unlikely(ipt->error || !ipt->nr_entries)) {




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