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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>
This commit is contained in:
NeilBrown 2014-08-08 14:19:54 -07:00 committed by Linus Torvalds
parent c312442fe3
commit 668128e90b
1 changed files with 6 additions and 2 deletions
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8
fs/autofs4/root.c
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@ -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;