On 9/4/19 4:22 PM, Jason Baron wrote:
> Currently, ep_poll_safewake() in the CONFIG_DEBUG_LOCK_ALLOC case uses
> ep_call_nested() in order to pass the correct subclass argument to
> spin_lock_irqsave_nested(). However, ep_call_nested() adds unnecessary
> checks for epoll depth and loops that are already verified when doing
> EPOLL_CTL_ADD. This mirrors a conversion that was done for
> !CONFIG_DEBUG_LOCK_ALLOC in: commit 37b5e5212a44 ("epoll: remove
> ep_call_nested() from ep_eventpoll_poll()")
>
> Signed-off-by: Jason Baron <jba...@akamai.com>
> Cc: Davidlohr Bueso <d...@stgolabs.net>
> Cc: Roman Penyaev <rpeny...@suse.de>
> Cc: Al Viro <v...@zeniv.linux.org.uk>
> Cc: Eric Wong <normalper...@yhbt.net>
> Cc: Andrew Morton <a...@linux-foundation.org>
> ---
> fs/eventpoll.c | 36 +++++++++++++-----------------------
> 1 file changed, 13 insertions(+), 23 deletions(-)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index d7f1f50..a9b2737 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -551,28 +551,23 @@ static int ep_call_nested(struct nested_calls *ncalls,
> */
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>
> -static struct nested_calls poll_safewake_ncalls;
> -
> -static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
> -{
> - unsigned long flags;
> - wait_queue_head_t *wqueue = (wait_queue_head_t *)cookie;
> -
> - spin_lock_irqsave_nested(&wqueue->lock, flags, call_nests + 1);
> - wake_up_locked_poll(wqueue, EPOLLIN);
> - spin_unlock_irqrestore(&wqueue->lock, flags);
> -
> - return 0;
> -}
> +static DEFINE_PER_CPU(int, wakeup_nest);
>
> static void ep_poll_safewake(wait_queue_head_t *wq)
> {
> - int this_cpu = get_cpu();
> -
> - ep_call_nested(&poll_safewake_ncalls,
> - ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
> + unsigned long flags;
> + int subclass;
>
> - put_cpu();
> + local_irq_save(flags);
> + preempt_disable();
> + subclass = __this_cpu_read(wakeup_nest);
> + spin_lock_nested(&wq->lock, subclass + 1);
> + __this_cpu_inc(wakeup_nest);
> + wake_up_locked_poll(wq, POLLIN);
> + __this_cpu_dec(wakeup_nest);
> + spin_unlock(&wq->lock);
> + local_irq_restore(flags);
> + preempt_enable();
> }
>
> #else
> @@ -2370,11 +2365,6 @@ static int __init eventpoll_init(void)
> */
> ep_nested_calls_init(&poll_loop_ncalls);
>
> -#ifdef CONFIG_DEBUG_LOCK_ALLOC
> - /* Initialize the structure used to perform safe poll wait head wake
> ups */
> - ep_nested_calls_init(&poll_safewake_ncalls);
> -#endif
> -
> /*
> * We can have many thousands of epitems, so prevent this from
> * using an extra cache line on 64-bit (and smaller) CPUs
>
Hi,
Any thoughts on this one?
Thanks,
-Jason
