Commit 0dd1e377 authored by Jan Stancek's avatar Jan Stancek Committed by Linus Torvalds

pipe: fix empty pipe check in pipe_write()

LTP pipeio_1 test is hanging with v5.5-rc2-385-gb8e382a1,
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: 1b6b26ae ("pipe: fix and clarify pipe write wakeup logic")
Reported-by: default avatarRachel Sibley <rasibley@redhat.com>
Signed-off-by: default avatarJan Stancek <jstancek@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b8e382a1
......@@ -581,7 +581,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
}
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);
......
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