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>

1 files changed, 20 insertions, 2 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index d54a99baf4f3..eb7c7255470c 100644
--- 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;
+                }
         }
 }