linux-kernel - [PATCH 6/6] autofs4: don't take spinlock when not needed in autofs4_lookup

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Date:	Thu, 10 Jul 2014 09:41:14 +1000
From:	NeilBrown <neilb@...e.de>
To:	Ian Kent <raven@...maw.net>
Cc:	autofs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 6/6] autofs4: don't take spinlock when not needed in
 autofs4_lookup_expiring

If the expiring_list is empty, we can avoid a costly spinlock
in the rcu-walk path through authfs4_d_manage.

Signed-off-by: NeilBrown <neilb@...e.de>
---
 fs/autofs4/root.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 1ad119407e2f..774c2dab331b 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -219,6 +219,8 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry,
 	const unsigned char *str = name->name;
 	struct list_head *p, *head;
 
+	if (list_empty(&sbi->expiring_list))
+		return NULL;
 	spin_lock(&sbi->lookup_lock);
 	head = &sbi->expiring_list;
 	list_for_each(p, head) {


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