watch_queue: Fix lack of barrier/sync/lock between post and read
There's nothing to synchronise post_one_notification() versus pipe_read(). Whilst posting is done under pipe->rd_wait.lock, the reader only takes pipe->mutex which cannot bar notification posting as that may need to be made from contexts that cannot sleep. Fix this by setting pipe->head with a barrier in post_one_notification() and reading pipe->head with a barrier in pipe_read(). If that's not sufficient, the rd_wait.lock will need to be taken, possibly in a ->confirm() op so that it only applies to notifications. The lock would, however, have to be dropped before copy_page_to_iter() is invoked. Fixes: c73be61c ("pipe: Add general notification queue support") Reported-by:Jann Horn <jannh@google.com> Signed-off-by:
David Howells <dhowells@redhat.com> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
parent
7ea1a012
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