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>
---
drivers/android/binder.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 1cdc7426bd033..0512af0f04646 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4788,23 +4788,20 @@ static int binder_thread_release(struct binder_proc *proc,
__release(&t->lock);
/*
- * 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, EPOLLHUP | 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();
--
2.34.1
