This is a note to let you know that I've just added the patch titled binder: use wake_up_pollfree() to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: binder-use-wake_up_pollfree.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sun Dec 12 02:47:18 PM CET 2021 From: Eric Biggers <ebiggers@xxxxxxxxxx> Date: Fri, 10 Dec 2021 16:19:25 -0800 Subject: binder: use wake_up_pollfree() To: stable@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Message-ID: <20211211001926.100856-3-ebiggers@xxxxxxxxxx> From: Eric Biggers <ebiggers@xxxxxxxxxx> commit a880b28a71e39013e357fd3adccd1d8a31bc69a8 upstream. wake_up_poll() uses nr_exclusive=1, so it's not guaranteed to wake up all exclusive waiters. Yet, POLLFREE *must* wake up all waiters. epoll and aio poll are fortunately not affected by this, but it's very fragile. Thus, the new function wake_up_pollfree() has been introduced. Convert binder to use wake_up_pollfree(). Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Fixes: f5cb779ba163 ("ANDROID: binder: remove waitqueue when thread exits.") Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20211209010455.42744-3-ebiggers@xxxxxxxxxx Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/android/binder.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4336,23 +4336,20 @@ static int binder_thread_release(struct } /* - * If this thread used poll, make sure we remove the waitqueue - * from any epoll data structures holding it with POLLFREE. - * waitqueue_active() is safe to use here because we're holding - * the inner lock. + * If this thread used poll, make sure we remove the waitqueue from any + * poll data structures holding it. */ - if ((thread->looper & BINDER_LOOPER_STATE_POLL) && - waitqueue_active(&thread->wait)) { - wake_up_poll(&thread->wait, POLLHUP | POLLFREE); - } + if (thread->looper & BINDER_LOOPER_STATE_POLL) + wake_up_pollfree(&thread->wait); binder_inner_proc_unlock(thread->proc); /* - * This is needed to avoid races between wake_up_poll() above and - * and ep_remove_waitqueue() called for other reasons (eg the epoll file - * descriptor being closed); ep_remove_waitqueue() holds an RCU read - * lock, so we can be sure it's done after calling synchronize_rcu(). + * This is needed to avoid races between wake_up_pollfree() above and + * someone else removing the last entry from the queue for other reasons + * (e.g. ep_remove_wait_queue() being called due to an epoll file + * descriptor being closed). Such other users hold an RCU read lock, so + * we can be sure they're done after we call synchronize_rcu(). */ if (thread->looper & BINDER_LOOPER_STATE_POLL) synchronize_rcu(); Patches currently in stable-queue which might be from ebiggers@xxxxxxxxxx are queue-4.14/binder-use-wake_up_pollfree.patch queue-4.14/wait-add-wake_up_pollfree.patch queue-4.14/signalfd-use-wake_up_pollfree.patch