linux-kernel - [PATCH 2/2] fs/epoll: loosen irq safety in epoll_insert() and epoll

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Date:   Fri, 20 Jul 2018 10:29:56 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     akpm@...ux-foundation.org
Cc:     jbaron@...mai.com, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 2/2] fs/epoll: loosen irq safety in epoll_insert() and epoll_remove()

Both functions are similar to the context of ep_modify(), called via
epoll_ctl(2). Just like ep_modify(), saving and restoring interrupts
is an overkill in these calls as it will never be called with irqs
disabled. While ep_remove() can be called directly from EPOLL_CTL_DEL,
it can also be called when releasing the file, but this also complies
with the above.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 fs/eventpoll.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 2247769eb941..1b1abc461fc0 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -762,7 +762,6 @@ static void epi_rcu_free(struct rcu_head *head)
  */
 static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 {
-	unsigned long flags;
 	struct file *file = epi->ffd.file;
 
 	/*
@@ -777,10 +776,10 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 
 	rb_erase_cached(&epi->rbn, &ep->rbr);
 
-	spin_lock_irqsave(&ep->wq.lock, flags);
+	spin_lock_irq(&ep->wq.lock);
 	if (ep_is_linked(&epi->rdllink))
 		list_del_init(&epi->rdllink);
-	spin_unlock_irqrestore(&ep->wq.lock, flags);
+	spin_unlock_irq(&ep->wq.lock);
 
 	wakeup_source_unregister(ep_wakeup_source(epi));
 	/*
@@ -1409,7 +1408,6 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 {
 	int error, pwake = 0;
 	__poll_t revents;
-	unsigned long flags;
 	long user_watches;
 	struct epitem *epi;
 	struct ep_pqueue epq;
@@ -1476,7 +1474,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 		goto error_remove_epi;
 
 	/* We have to drop the new item inside our item list to keep track of it */
-	spin_lock_irqsave(&ep->wq.lock, flags);
+	spin_lock_irq(&ep->wq.lock);
 
 	/* record NAPI ID of new item if present */
 	ep_set_busy_poll_napi_id(epi);
@@ -1493,7 +1491,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 			pwake++;
 	}
 
-	spin_unlock_irqrestore(&ep->wq.lock, flags);
+	spin_unlock_irq(&ep->wq.lock);
 
 	atomic_long_inc(&ep->user->epoll_watches);
 
@@ -1519,10 +1517,10 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 	 * list, since that is used/cleaned only inside a section bound by "mtx".
 	 * And ep_insert() is called with "mtx" held.
 	 */
-	spin_lock_irqsave(&ep->wq.lock, flags);
+	spin_lock_irq(&ep->wq.lock);
 	if (ep_is_linked(&epi->rdllink))
 		list_del_init(&epi->rdllink);
-	spin_unlock_irqrestore(&ep->wq.lock, flags);
+	spin_unlock_irq(&ep->wq.lock);
 
 	wakeup_source_unregister(ep_wakeup_source(epi));
 
-- 
2.16.4