Messages in this thread | | | Subject | Re: [PATCH] epoll: simplify ep_poll_safewake() for CONFIG_DEBUG_LOCK_ALLOC | From | Jason Baron <> | Date | Tue, 24 Sep 2019 13:34:58 -0400 |
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On 9/23/19 3:23 PM, Roman Penyaev wrote: > On 2019-09-23 17:43, Jason Baron wrote: >> 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 <jbaron@akamai.com> >>> Cc: Davidlohr Bueso <dave@stgolabs.net> >>> Cc: Roman Penyaev <rpenyaev@suse.de> >>> Cc: Al Viro <viro@zeniv.linux.org.uk> >>> Cc: Eric Wong <normalperson@yhbt.net> >>> Cc: Andrew Morton <akpm@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(); >>> } > > What if reduce number of lines with something as the following: > > int this_cpu = get_cpu(); > subclass = __this_cpu_inc_return(wakeup_nest); > spin_lock_irqsave_nested(&wq->lock, flags, subclass); > wake_up_locked_poll(wq, POLLIN); > spin_unlock_irqrestore(&wq->lock, flags); > __this_cpu_dec(wakeup_nest); > put_cpu(); > > Other than that looks good to me. > > Reviewed-by: Roman Penyaev <rpenyaev@suse.de> > > -- > Roman
Hi,
I put the local_irq_save(flags), call there first so that there wouldn't be any nesting. For example, in your sequence, there could be an irq after the __this_cpu_inc_return(), that could end up back here.
I still can use __this_cpu_inc_return() to simplify things a bit.
Thanks,
-Jason
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