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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Cc: asml.silence@gmail.com
Subject: [PATCH 2/2] io_uring: remove double poll entry on arm failure
Date: Tue, 20 Jul 2021 10:50:44 +0100	[thread overview]
Message-ID: <0ec1228fc5eda4cb524eeda857da8efdc43c331c.1626774457.git.asml.silence@gmail.com> (raw)
In-Reply-To: <cover.1626774457.git.asml.silence@gmail.com>

__io_queue_proc() can enqueue both poll entries and still fail
afterwards, so the callers trying to cancel it should also try to remove
the second poll entry (if any).

For example, it may leave the request alive referencing a io_uring
context but not accessible for cancellation:

[  282.599913][ T1620] task:iou-sqp-23145   state:D stack:28720 pid:23155 ppid:  8844 flags:0x00004004
[  282.609927][ T1620] Call Trace:
[  282.613711][ T1620]  __schedule+0x93a/0x26f0
[  282.634647][ T1620]  schedule+0xd3/0x270
[  282.638874][ T1620]  io_uring_cancel_generic+0x54d/0x890
[  282.660346][ T1620]  io_sq_thread+0xaac/0x1250
[  282.696394][ T1620]  ret_from_fork+0x1f/0x30

Cc: stable@vger.kernel.org
Fixes: 18bceab101add ("io_uring: allow POLL_ADD with double poll_wait() users")
Reported-and-tested-by: syzbot+ac957324022b7132accf@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6668902cf50c..6486b54a0f62 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5113,6 +5113,8 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
 		ipt->error = -EINVAL;
 
 	spin_lock_irq(&ctx->completion_lock);
+	if (ipt->error)
+		io_poll_remove_double(req);
 	if (likely(poll->head)) {
 		spin_lock(&poll->head->lock);
 		if (unlikely(list_empty(&poll->wait.entry))) {
-- 
2.32.0


  parent reply	other threads:[~2021-07-20  9:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20  9:50 [PATCH 0/2] double poll fixes Pavel Begunkov
2021-07-20  9:50 ` [PATCH 1/2] io_uring: explicitly count entries for poll reqs Pavel Begunkov
2021-07-20  9:50 ` Pavel Begunkov [this message]
2021-07-20 13:50 ` [PATCH 0/2] double poll fixes Jens Axboe

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