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Date: Sun, 22 Dec 2019 13:33:24 +0100 From: Jan Stancek <jstancek@...hat.com> To: torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org Cc: linux-kernel@...r.kernel.org, dhowells@...hat.com, viro@...iv.linux.org.uk, rasibley@...hat.com, jstancek@...hat.com Subject: [PATCH] pipe: fix empty pipe check in pipe_write() LTP pipeio_1 test is hanging with v5.5-rc2-385-gb8e382a185eb, with read side observing empty pipe and sleeping and write side running out of space and then sleeping as well. In this scenario there are 5 writers and 1 reader. Problem is that after pipe_write() reacquires pipe lock, it re-checks for empty pipe with potentially stale 'head' and doesn't wake up read side anymore. pipe->tail can advance beyond 'head', because there are multiple writers. Use pipe->head for empty pipe check after reacquiring lock to observe current state. Testing: With patch, LTP pipeio_1 ran successfully in loop for 1 hour. Without patch it hanged within a minute. Fixes: 1b6b26ae7053 ("pipe: fix and clarify pipe write wakeup logic") Reported-by: Rachel Sibley <rasibley@...hat.com> Signed-off-by: Jan Stancek <jstancek@...hat.com> --- fs/pipe.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/pipe.c b/fs/pipe.c index 04d004ee2e8c..57502c3c0fba 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -581,7 +581,7 @@ static inline bool pipe_writable(const struct pipe_inode_info *pipe) } wait_event_interruptible(pipe->wait, pipe_writable(pipe)); __pipe_lock(pipe); - was_empty = pipe_empty(head, pipe->tail); + was_empty = pipe_empty(pipe->head, pipe->tail); } out: __pipe_unlock(pipe); -- 1.8.3.1
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