[patch 46/86] epoll: simplify ep_poll_safewake() for CONFIG_DEBUG_LOCK_ALLOC

Andrew Morton
2019-12-05T00:52:15Z

From: Jason Baron <jbaron@akamai.com>
Subject: epoll: simplify ep_poll_safewake() for CONFIG_DEBUG_LOCK_ALLOC

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()")

Link: http://lkml.kernel.org/r/1567628549-11501-1-git-send-email-jbaron@akamai.com
Signed-off-by: Jason Baron <jbaron@akamai.com>
Reviewed-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/eventpoll.c | 36 +++++++++++++-----------------------
1 file changed, 13 insertions(+), 23 deletions(-)

--- a/fs/eventpoll.c~epoll-simplify-ep_poll_safewake-for-config_debug_lock_alloc
+++ a/fs/eventpoll.c
@@ -551,28 +551,23 @@ out_unlock:
*/
#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
_