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authorIan Kent <raven@themaw.net>2008-07-23 21:30:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-24 10:47:31 -0700
commit2576737873dc1d9ea461a5955a5f6779b569a350 (patch)
treeaad8f5cf52c872f307275328022a3bcb94a6c342 /fs/autofs4/autofs_i.h
parentautofs4: revert - redo lookup in ttfd (diff)
downloadlinux-dev-2576737873dc1d9ea461a5955a5f6779b569a350.tar.xz
linux-dev-2576737873dc1d9ea461a5955a5f6779b569a350.zip
autofs4: use look aside list for lookups
A while ago a patch to resolve a deadlock during directory creation was merged. This delayed the hashing of lookup dentrys until the ->mkdir() (or ->symlink()) operation completed to ensure we always went through ->lookup() instead of also having processes go through ->revalidate() so our VFS locking remained consistent. Now we are seeing a couple of side affects of that change in situations with heavy mount activity. Two cases have been identified: 1) When a mount request is triggered, due to the delayed hashing, the directory created by user space for the mount point doesn't have the DCACHE_AUTOFS_PENDING flag set. In the case of an autofs multi-mount where a tree of mount point directories are created this can lead to the path walk continuing rather than the dentry being sent to the wait queue to wait for request completion. This is because, if the pending flag isn't set, the criteria for deciding this is a mount in progress fails to hold, namely that the dentry is not a mount point and has no subdirectories. 2) A mount request dentry is initially created negative and unhashed. It remains this way until the ->mkdir() callback completes. Since it is unhashed a fresh dentry is used when the user space mount request creates the mount point directory. This leaves the original dentry negative and unhashed. But revalidate has no way to tell the VFS that the dentry has changed, other than to force another ->lookup() by returning false, which is at best wastefull and at worst not possible. This results in an -ENOENT return from the original path walk when in fact the mount succeeded. To resolve this we need to ensure that the same dentry is used in all calls to ->lookup() during the course of a mount request. This patch achieves that by adding the initial dentry to a look aside list and removes it at ->mkdir() or ->symlink() completion (or when the dentry is released), since these are the only create operations autofs4 supports. Signed-off-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')
-rw-r--r--fs/autofs4/autofs_i.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index 69b1497b0029..2dce2334737d 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -52,6 +52,7 @@ struct autofs_info {
int flags;
+ struct list_head active;
struct list_head expiring;
struct autofs_sb_info *sbi;
@@ -113,6 +114,7 @@ struct autofs_sb_info {
spinlock_t fs_lock;
struct autofs_wait_queue *queues; /* Wait queue pointer */
spinlock_t lookup_lock;
+ struct list_head active_list;
struct list_head expiring_list;
};