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-rw-r--r--fs/dcache.c66
1 files changed, 60 insertions, 6 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index 940d188e5d14..385f5dbc4b0c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -382,6 +382,8 @@ static inline void prune_one_dentry(struct dentry * dentry)
/**
* prune_dcache - shrink the dcache
* @count: number of entries to try and free
+ * @sb: if given, ignore dentries for other superblocks
+ * which are being unmounted.
*
* Shrink the dcache. This is done when we need
* more memory, or simply when we need to unmount
@@ -392,16 +394,29 @@ static inline void prune_one_dentry(struct dentry * dentry)
* all the dentries are in use.
*/
-static void prune_dcache(int count)
+static void prune_dcache(int count, struct super_block *sb)
{
spin_lock(&dcache_lock);
for (; count ; count--) {
struct dentry *dentry;
struct list_head *tmp;
+ struct rw_semaphore *s_umount;
cond_resched_lock(&dcache_lock);
tmp = dentry_unused.prev;
+ if (unlikely(sb)) {
+ /* Try to find a dentry for this sb, but don't try
+ * too hard, if they aren't near the tail they will
+ * be moved down again soon
+ */
+ int skip = count;
+ while (skip && tmp != &dentry_unused &&
+ list_entry(tmp, struct dentry, d_lru)->d_sb != sb) {
+ skip--;
+ tmp = tmp->prev;
+ }
+ }
if (tmp == &dentry_unused)
break;
list_del_init(tmp);
@@ -427,7 +442,45 @@ static void prune_dcache(int count)
spin_unlock(&dentry->d_lock);
continue;
}
- prune_one_dentry(dentry);
+ /*
+ * If the dentry is not DCACHED_REFERENCED, it is time
+ * to remove it from the dcache, provided the super block is
+ * NULL (which means we are trying to reclaim memory)
+ * or this dentry belongs to the same super block that
+ * we want to shrink.
+ */
+ /*
+ * If this dentry is for "my" filesystem, then I can prune it
+ * without taking the s_umount lock (I already hold it).
+ */
+ if (sb && dentry->d_sb == sb) {
+ prune_one_dentry(dentry);
+ continue;
+ }
+ /*
+ * ...otherwise we need to be sure this filesystem isn't being
+ * unmounted, otherwise we could race with
+ * generic_shutdown_super(), and end up holding a reference to
+ * an inode while the filesystem is unmounted.
+ * So we try to get s_umount, and make sure s_root isn't NULL.
+ * (Take a local copy of s_umount to avoid a use-after-free of
+ * `dentry').
+ */
+ s_umount = &dentry->d_sb->s_umount;
+ if (down_read_trylock(s_umount)) {
+ if (dentry->d_sb->s_root != NULL) {
+ prune_one_dentry(dentry);
+ up_read(s_umount);
+ continue;
+ }
+ up_read(s_umount);
+ }
+ spin_unlock(&dentry->d_lock);
+ /* Cannot remove the first dentry, and it isn't appropriate
+ * to move it to the head of the list, so give up, and try
+ * later
+ */
+ break;
}
spin_unlock(&dcache_lock);
}
@@ -630,7 +683,7 @@ void shrink_dcache_parent(struct dentry * parent)
int found;
while ((found = select_parent(parent)) != 0)
- prune_dcache(found);
+ prune_dcache(found, parent->d_sb);
}
/**
@@ -643,9 +696,10 @@ void shrink_dcache_parent(struct dentry * parent)
* done under dcache_lock.
*
*/
-void shrink_dcache_anon(struct hlist_head *head)
+void shrink_dcache_anon(struct super_block *sb)
{
struct hlist_node *lp;
+ struct hlist_head *head = &sb->s_anon;
int found;
do {
found = 0;
@@ -668,7 +722,7 @@ void shrink_dcache_anon(struct hlist_head *head)
}
}
spin_unlock(&dcache_lock);
- prune_dcache(found);
+ prune_dcache(found, sb);
} while(found);
}
@@ -689,7 +743,7 @@ static int shrink_dcache_memory(int nr, gfp_t gfp_mask)
if (nr) {
if (!(gfp_mask & __GFP_FS))
return -1;
- prune_dcache(nr);
+ prune_dcache(nr, NULL);
}
return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;
}