--- /dev/null
+From foo@baz Sun Dec 12 02:49:35 PM CET 2021
+From: Eric Biggers <ebiggers@kernel.org>
+Date: Fri, 10 Dec 2021 16:28:31 -0800
+Subject: binder: use wake_up_pollfree()
+To: stable@vger.kernel.org
+Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
+Message-ID: <20211211002832.153742-3-ebiggers@kernel.org>
+
+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
+@@ -2623,21 +2623,18 @@ static int binder_free_thread(struct bin
+ }
+
+ /*
+- * 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 global 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);
+
+ /*
+- * 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();
--- /dev/null
+From foo@baz Sun Dec 12 02:49:35 PM CET 2021
+From: Eric Biggers <ebiggers@kernel.org>
+Date: Fri, 10 Dec 2021 16:28:32 -0800
+Subject: signalfd: use wake_up_pollfree()
+To: stable@vger.kernel.org
+Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
+Message-ID: <20211211002832.153742-4-ebiggers@kernel.org>
+
+From: Eric Biggers <ebiggers@google.com>
+
+commit 9537bae0da1f8d1e2361ab6d0479e8af7824e160 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 signalfd to use wake_up_pollfree().
+
+Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
+Fixes: d80e731ecab4 ("epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()")
+Cc: stable@vger.kernel.org
+Link: https://lore.kernel.org/r/20211209010455.42744-4-ebiggers@kernel.org
+Signed-off-by: Eric Biggers <ebiggers@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ fs/signalfd.c | 12 +-----------
+ 1 file changed, 1 insertion(+), 11 deletions(-)
+
+--- a/fs/signalfd.c
++++ b/fs/signalfd.c
+@@ -34,17 +34,7 @@
+
+ void signalfd_cleanup(struct sighand_struct *sighand)
+ {
+- wait_queue_head_t *wqh = &sighand->signalfd_wqh;
+- /*
+- * The lockless check can race with remove_wait_queue() in progress,
+- * but in this case its caller should run under rcu_read_lock() and
+- * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
+- */
+- if (likely(!waitqueue_active(wqh)))
+- return;
+-
+- /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
+- wake_up_poll(wqh, POLLHUP | POLLFREE);
++ wake_up_pollfree(&sighand->signalfd_wqh);
+ }
+
+ struct signalfd_ctx {
--- /dev/null
+From foo@baz Sun Dec 12 02:49:35 PM CET 2021
+From: Eric Biggers <ebiggers@kernel.org>
+Date: Fri, 10 Dec 2021 16:28:30 -0800
+Subject: wait: add wake_up_pollfree()
+To: stable@vger.kernel.org
+Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
+Message-ID: <20211211002832.153742-2-ebiggers@kernel.org>
+
+From: Eric Biggers <ebiggers@google.com>
+
+commit 42288cb44c4b5fff7653bc392b583a2b8bd6a8c0 upstream.
+
+Several ->poll() implementations are special in that they use a
+waitqueue whose lifetime is the current task, rather than the struct
+file as is normally the case. This is okay for blocking polls, since a
+blocking poll occurs within one task; however, non-blocking polls
+require another solution. This solution is for the queue to be cleared
+before it is freed, using 'wake_up_poll(wq, EPOLLHUP | POLLFREE);'.
+
+However, that has a bug: wake_up_poll() calls __wake_up() with
+nr_exclusive=1. Therefore, if there are multiple "exclusive" waiters,
+and the wakeup function for the first one returns a positive value, only
+that one will be called. That's *not* what's needed for POLLFREE;
+POLLFREE is special in that it really needs to wake up everyone.
+
+Considering the three non-blocking poll systems:
+
+- io_uring poll doesn't handle POLLFREE at all, so it is broken anyway.
+
+- aio poll is unaffected, since it doesn't support exclusive waits.
+ However, that's fragile, as someone could add this feature later.
+
+- epoll doesn't appear to be broken by this, since its wakeup function
+ returns 0 when it sees POLLFREE. But this is fragile.
+
+Although there is a workaround (see epoll), it's better to define a
+function which always sends POLLFREE to all waiters. Add such a
+function. Also make it verify that the queue really becomes empty after
+all waiters have been woken up.
+
+Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
+Cc: stable@vger.kernel.org
+Link: https://lore.kernel.org/r/20211209010455.42744-2-ebiggers@kernel.org
+Signed-off-by: Eric Biggers <ebiggers@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ include/linux/wait.h | 26 ++++++++++++++++++++++++++
+ kernel/sched/wait.c | 8 ++++++++
+ 2 files changed, 34 insertions(+)
+
+--- a/include/linux/wait.h
++++ b/include/linux/wait.h
+@@ -151,6 +151,7 @@ void __wake_up_locked_key(wait_queue_hea
+ void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode, int nr, void *key);
+ void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr);
+ void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr);
++void __wake_up_pollfree(wait_queue_head_t *wq_head);
+ void __wake_up_bit(wait_queue_head_t *, void *, int);
+ int __wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
+ int __wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
+@@ -185,6 +186,31 @@ wait_queue_head_t *bit_waitqueue(void *,
+ #define wake_up_interruptible_sync_poll(x, m) \
+ __wake_up_sync_key((x), TASK_INTERRUPTIBLE, 1, (void *) (m))
+
++/**
++ * wake_up_pollfree - signal that a polled waitqueue is going away
++ * @wq_head: the wait queue head
++ *
++ * In the very rare cases where a ->poll() implementation uses a waitqueue whose
++ * lifetime is tied to a task rather than to the 'struct file' being polled,
++ * this function must be called before the waitqueue is freed so that
++ * non-blocking polls (e.g. epoll) are notified that the queue is going away.
++ *
++ * The caller must also RCU-delay the freeing of the wait_queue_head, e.g. via
++ * an explicit synchronize_rcu() or call_rcu(), or via SLAB_DESTROY_BY_RCU.
++ */
++static inline void wake_up_pollfree(wait_queue_head_t *wq_head)
++{
++ /*
++ * For performance reasons, we don't always take the queue lock here.
++ * Therefore, we might race with someone removing the last entry from
++ * the queue, and proceed while they still hold the queue lock.
++ * However, rcu_read_lock() is required to be held in such cases, so we
++ * can safely proceed with an RCU-delayed free.
++ */
++ if (waitqueue_active(wq_head))
++ __wake_up_pollfree(wq_head);
++}
++
+ #define ___wait_cond_timeout(condition) \
+ ({ \
+ bool __cond = (condition); \
+--- a/kernel/sched/wait.c
++++ b/kernel/sched/wait.c
+@@ -10,6 +10,7 @@
+ #include <linux/wait.h>
+ #include <linux/hash.h>
+ #include <linux/kthread.h>
++#include <linux/poll.h>
+
+ void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
+ {
+@@ -156,6 +157,13 @@ void __wake_up_sync(wait_queue_head_t *q
+ }
+ EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
+
++void __wake_up_pollfree(wait_queue_head_t *wq_head)
++{
++ __wake_up(wq_head, TASK_NORMAL, 0, (void *)(POLLHUP | POLLFREE));
++ /* POLLFREE must have cleared the queue. */
++ WARN_ON_ONCE(waitqueue_active(wq_head));
++}
++
+ /*
+ * Note: we use "set_current_state()" _after_ the wait-queue add,
+ * because we need a memory barrier there on SMP, so that any
projects / thirdparty / kernel / stable-queue.git / commitdiff
