From cdcdbbdc084e4097ac13cda194ff7e5afc96a862 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Fri, 8 Aug 2014 14:19:54 -0700
Subject: [PATCH] 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 autofs4_d_manage (once the rest of the path
becomes rcu-walk friendly).
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/autofs4/root.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index cc87c1abac971..fb202cadd4b32 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -166,8 +166,10 @@ static struct dentry *autofs4_lookup_active(struct dentry *dentry)
const unsigned char *str = name->name;
struct list_head *p, *head;
- spin_lock(&sbi->lookup_lock);
head = &sbi->active_list;
+ if (list_empty(head))
+ return NULL;
+ spin_lock(&sbi->lookup_lock);
list_for_each(p, head) {
struct autofs_info *ino;
struct dentry *active;
@@ -218,8 +220,10 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)
const unsigned char *str = name->name;
struct list_head *p, *head;
- spin_lock(&sbi->lookup_lock);
head = &sbi->expiring_list;
+ if (list_empty(head))
+ return NULL;
+ spin_lock(&sbi->lookup_lock);
list_for_each(p, head) {
struct autofs_info *ino;
struct dentry *expiring;
--
2.39.5