path: root/fs/autofs4
diff options
authorNeilBrown <neilb@suse.de>2014-10-13 15:52:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-14 02:18:16 +0200
commitef16cc5909c907586f4eba5455e183fd319637c8 (patch)
tree8c85bca785379b19f215b210a89717e7cd51c4c8 /fs/autofs4
parentautofs4: avoid taking fs_lock during rcu-walk (diff)
autofs4: d_manage() should return -EISDIR when appropriate in rcu-walk mode.
If rcu-walk mode we don't *have* to return -EISDIR for non-mount-traps as we will simply drop into REF-walk and handling DCACHE_NEED_AUTOMOUNT dentrys the slow way. But it is better if we do when possible. In 'oz_mode', use the same condition as ref-walk: if not a mountpoint, then it must be -EISDIR. In regular mode there are most tests needed. Most of them can be performed without taking any spinlocks. If we find a directory that isn't obviously empty, and isn't mounted on, we need to call 'simple_empty()' which does take a spinlock. If this turned out to hurt performance, some other approach could be found to signal when a directory is known to be empty. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Ian Kent <raven@themaw.net> Tested-by: Ian Kent <raven@themaw.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/autofs4')
1 files changed, 20 insertions, 6 deletions
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 2296c8301b66..d76d083f2f06 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -433,8 +433,6 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
/* The daemon never waits. */
if (autofs4_oz_mode(sbi)) {
- if (rcu_walk)
- return 0;
if (!d_mountpoint(dentry))
return -EISDIR;
return 0;
@@ -452,12 +450,28 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
if (status)
return status;
- if (rcu_walk)
- /* it is always safe to return 0 as the worst that
- * will happen is we retry in REF-walk mode.
- * Better than always taking a lock.
+ if (rcu_walk) {
+ /* We don't need fs_lock in rcu_walk mode,
+ * just testing 'AUTOFS_INFO_NO_RCU' is enough.
+ * simple_empty() takes a spinlock, so leave it
+ * to last.
+ * We only return -EISDIR when certain this isn't
+ * a mount-trap.
+ struct inode *inode;
+ return 0;
+ if (d_mountpoint(dentry))
+ return 0;
+ inode = ACCESS_ONCE(dentry->d_inode);
+ if (inode && S_ISLNK(inode->i_mode))
+ return -EISDIR;
+ if (list_empty(&dentry->d_subdirs))
+ return 0;
+ if (!simple_empty(dentry))
+ return -EISDIR;
return 0;
+ }