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authorJan Stancek <jstancek@redhat.com>2019-12-22 13:33:24 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2019-12-22 09:47:47 -0800
commit0dd1e3773ae8afc4bfdce782bdeffc10f9cae6ec (patch)
tree65b6d77c5be91eb0104945af6598bf8d9718426e /include
parentMerge tag 'trace-v5.5-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace (diff)
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@redhat.com> Signed-off-by: Jan Stancek <jstancek@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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