linux-kernel - [PATCH v2 2/4] epoll: loosen irq safety in ep_poll

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Message-Id: <20190103150104.17128-3-rpenyaev@suse.de>
Date:   Thu,  3 Jan 2019 16:01:02 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Roman Penyaev <rpenyaev@...e.de>, Davidlohr Bueso <dbueso@...e.de>,
        Jason Baron <jbaron@...mai.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/4] epoll: loosen irq safety in ep_poll_callback()

Callers of the ep_poll_callback() (all set of wake_up_*poll()) disable
interrupts, so no need to save/restore irq flags.

Signed-off-by: Roman Penyaev <rpenyaev@...e.de>
Cc: Davidlohr Bueso <dbueso@...e.de>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 fs/eventpoll.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 3627c2e07149..3c373a510f65 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1124,13 +1124,18 @@ struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
 static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
 {
 	int pwake = 0;
-	unsigned long flags;
 	struct epitem *epi = ep_item_from_wait(wait);
 	struct eventpoll *ep = epi->ep;
 	__poll_t pollflags = key_to_poll(key);
 	int ewake = 0;
 
-	spin_lock_irqsave(&ep->wq.lock, flags);
+	/*
+	 * Called by irq context or interrupts are disabled by the wake_up_*poll
+	 * callers.
+	 */
+	lockdep_assert_irqs_disabled();
+
+	spin_lock(&ep->wq.lock);
 
 	ep_set_busy_poll_napi_id(epi);
 
@@ -1207,7 +1212,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
 		pwake++;
 
 out_unlock:
-	spin_unlock_irqrestore(&ep->wq.lock, flags);
+	spin_unlock(&ep->wq.lock);
 
 	/* We have to call this outside the lock */
 	if (pwake)
-- 
2.19.1