From 668128e90b9596668141539326178dacc42af188 Mon Sep 17 00:00:00 2001 From: NeilBrown 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 Reviewed-by: Ian Kent Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 cc87c1a..fb202ca 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; -- 2.7.4