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    Subject[PATCH 4.14 24/53] binder: use wake_up_pollfree()
    Date
    From: Eric Biggers <ebiggers@google.com>

    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@linux-foundation.org>
    Fixes: f5cb779ba163 ("ANDROID: binder: remove waitqueue when thread exits.")
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20211209010455.42744-3-ebiggers@kernel.org
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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();

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