diff options
| -rw-r--r-- | fs/dcache.c | 53 |
1 files changed, 41 insertions, 12 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index c23f78a9d15..d54a99baf4f 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -530,6 +530,38 @@ failed: return dentry; /* try again with same dentry */ } +static inline struct dentry *lock_parent(struct dentry *dentry) +{ + struct dentry *parent = dentry->d_parent; + if (IS_ROOT(dentry)) + return NULL; + if (likely(spin_trylock(&parent->d_lock))) + return parent; + spin_unlock(&dentry->d_lock); + rcu_read_lock(); +again: + parent = ACCESS_ONCE(dentry->d_parent); + spin_lock(&parent->d_lock); + /* + * We can't blindly lock dentry until we are sure + * that we won't violate the locking order. + * Any changes of dentry->d_parent must have + * been done with parent->d_lock held, so + * spin_lock() above is enough of a barrier + * for checking if it's still our child. + */ + if (unlikely(parent != dentry->d_parent)) { + spin_unlock(&parent->d_lock); + goto again; + } + rcu_read_unlock(); + if (parent != dentry) + spin_lock(&dentry->d_lock); + else + parent = NULL; + return parent; +} + /* * This is dput * @@ -804,6 +836,8 @@ static void shrink_dentry_list(struct list_head *list) struct inode *inode; dentry = list_entry(list->prev, struct dentry, d_lru); spin_lock(&dentry->d_lock); + parent = lock_parent(dentry); + /* * The dispose list is isolated and dentries are not accounted * to the LRU here, so we can simply remove it from the list @@ -817,6 +851,8 @@ static void shrink_dentry_list(struct list_head *list) */ if ((int)dentry->d_lockref.count > 0) { spin_unlock(&dentry->d_lock); + if (parent) + spin_unlock(&parent->d_lock); continue; } @@ -824,6 +860,8 @@ static void shrink_dentry_list(struct list_head *list) if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) { bool can_free = dentry->d_flags & DCACHE_MAY_FREE; spin_unlock(&dentry->d_lock); + if (parent) + spin_unlock(&parent->d_lock); if (can_free) dentry_free(dentry); continue; @@ -833,22 +871,13 @@ static void shrink_dentry_list(struct list_head *list) if (inode && unlikely(!spin_trylock(&inode->i_lock))) { d_shrink_add(dentry, list); spin_unlock(&dentry->d_lock); + if (parent) + spin_unlock(&parent->d_lock); continue; } - parent = NULL; - if (!IS_ROOT(dentry)) { - parent = dentry->d_parent; - if (unlikely(!spin_trylock(&parent->d_lock))) { - if (inode) - spin_unlock(&inode->i_lock); - d_shrink_add(dentry, list); - spin_unlock(&dentry->d_lock); - continue; - } - } - __dentry_kill(dentry); + /* * We need to prune ancestors too. This is necessary to prevent * quadratic behavior of shrink_dcache_parent(), but is also |