path: root/fs/autofs4/autofs_i.h
diff options
authorNeilBrown <neilb@suse.de>2014-10-13 15:52:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-14 02:18:16 +0200
commit4d885f90e3784df77945101d8ec32dc798a49862 (patch)
treea034e761a43d14bb24f27e98a0cd3f568bbf7732 /fs/autofs4/autofs_i.h
parentautofs4: make "autofs4_can_expire" idempotent. (diff)
autofs4: avoid taking fs_lock during rcu-walk
->fs_lock protects AUTOFS_INF_EXPIRING. We need to be sure that once the flag is set, no new references beneath the dentry are taken. So rcu-walk currently needs to take fs_lock before checking the flag. This hurts performance. Change the expiry to a two-stage process. First set AUTOFS_INF_NO_RCU which forces any path walk into ref-walk mode, then drop the lock and call synchronize_rcu(). Once that returns we can be sure no rcu-walk is active beneath the dentry and we can check reference counts again. Now during an RCU-walk we can test AUTOFS_INF_EXPIRING without taking the lock as along as we test AUTOFS_INF_NO_RCU too. If either are set, we must abort the RCU-walk If neither are set, we know that refcounts will be tested again after we finish the RCU-walk so we are safe to continue. ->fs_lock is still taken in d_manage() to check for a non-trap directory. That will be resolved in the next patch. 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/autofs_i.h')
1 files changed, 4 insertions, 0 deletions
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index 2f1032f12d91..8e98cf954bab 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -79,6 +79,10 @@ struct autofs_info {
#define AUTOFS_INF_EXPIRING (1<<0) /* dentry is in the process of expiring */
+#define AUTOFS_INF_NO_RCU (1<<1) /* the dentry is being considered
+ * for expiry, so RCU_walk is
+ * not permitted
+ */
#define AUTOFS_INF_PENDING (1<<2) /* dentry pending mount */
struct autofs_wait_queue {