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    Subject[PATCH 4.9 21/42] signalfd: use wake_up_pollfree()
    Date
    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 {

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