dealing with the rest of shrink_dentry_list() livelock

We have the same problem with ->d_lock order in the inner loop, where
we are dropping references to ancestors.  Same solution, basically -
instead of using dentry_kill() we use lock_parent() (introduced in the
previous commit) to get that lock in a safe way, recheck ->d_count
(in case if lock_parent() has ended up dropping and retaking ->d_lock
and somebody managed to grab a reference during that window), trylock
the inode->i_lock and use __dentry_kill() to do the rest.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index d54a99baf4f314d43bf1d79abf814da0ff3bef01..eb7c7255470cdf8341fe72fb9f63d8e68d759ca3 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -885,8 +885,26 @@ static void shrink_dentry_list(struct list_head *list)
                 * fragmentation.
                 */
                dentry = parent;
-               while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
-                       dentry = dentry_kill(dentry, 1);
+               while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
+                       parent = lock_parent(dentry);
+                       if (dentry->d_lockref.count != 1) {
+                               dentry->d_lockref.count--;
+                               spin_unlock(&dentry->d_lock);
+                               if (parent)
+                                       spin_unlock(&parent->d_lock);
+                               break;
+                       }
+                       inode = dentry->d_inode;        /* can't be NULL */
+                       if (unlikely(!spin_trylock(&inode->i_lock))) {
+                               spin_unlock(&dentry->d_lock);
+                               if (parent)
+                                       spin_unlock(&parent->d_lock);
+                               cpu_relax();
+                               continue;
+                       }
+                       __dentry_kill(dentry);
+                       dentry = parent;
+               }
        }
 }