1 files changed, 106 insertions, 38 deletions

diff --git a/fs/super.c b/fs/super.c
index 672538ca9831..50728d9c1a05 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -37,6 +37,7 @@
 #include <linux/user_namespace.h>
 #include "internal.h"
 
+static int thaw_super_locked(struct super_block *sb);
 
 static LIST_HEAD(super_blocks);
 static DEFINE_SPINLOCK(sb_lock);
@@ -120,13 +121,23 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 	sb = container_of(shrink, struct super_block, s_shrink);
 
 	/*
-	 * Don't call trylock_super as it is a potential
-	 * scalability bottleneck. The counts could get updated
-	 * between super_cache_count and super_cache_scan anyway.
-	 * Call to super_cache_count with shrinker_rwsem held
-	 * ensures the safety of call to list_lru_shrink_count() and
-	 * s_op->nr_cached_objects().
+	 * We don't call trylock_super() here as it is a scalability bottleneck,
+	 * so we're exposed to partial setup state. The shrinker rwsem does not
+	 * protect filesystem operations backing list_lru_shrink_count() or
+	 * s_op->nr_cached_objects(). Counts can change between
+	 * super_cache_count and super_cache_scan, so we really don't need locks
+	 * here.
+	 *
+	 * However, if we are currently mounting the superblock, the underlying
+	 * filesystem might be in a state of partial construction and hence it
+	 * is dangerous to access it.  trylock_super() uses a SB_BORN check to
+	 * avoid this situation, so do the same here. The memory barrier is
+	 * matched with the one in mount_fs() as we don't hold locks here.
 	 */
+	if (!(sb->s_flags & SB_BORN))
+		return 0;
+	smp_rmb();
+
 	if (sb->s_op && sb->s_op->nr_cached_objects)
 		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 
@@ -166,6 +177,7 @@ static void destroy_unused_super(struct super_block *s)
 	security_sb_free(s);
 	put_user_ns(s->s_user_ns);
 	kfree(s->s_subtype);
+	free_prealloced_shrinker(&s->s_shrink);
 	/* no delays needed */
 	destroy_super_work(&s->destroy_work);
 }
@@ -251,6 +263,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_shrink.count_objects = super_cache_count;
 	s->s_shrink.batch = 1024;
 	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
+	if (prealloc_shrinker(&s->s_shrink))
+		goto fail;
 	return s;
 
 fail:
@@ -517,11 +531,7 @@ retry:
 	hlist_add_head(&s->s_instances, &type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(type);
-	err = register_shrinker(&s->s_shrink);
-	if (err) {
-		deactivate_locked_super(s);
-		s = ERR_PTR(err);
-	}
+	register_shrinker_prepared(&s->s_shrink);
 	return s;
 }
 
@@ -574,6 +584,28 @@ void drop_super_exclusive(struct super_block *sb)
 }
 EXPORT_SYMBOL(drop_super_exclusive);
 
+static void __iterate_supers(void (*f)(struct super_block *))
+{
+	struct super_block *sb, *p = NULL;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		f(sb);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+}
 /**
  *	iterate_supers - call function for all active superblocks
  *	@f: function to call
@@ -881,33 +913,22 @@ cancel_readonly:
 	return retval;
 }
 
-static void do_emergency_remount(struct work_struct *work)
+static void do_emergency_remount_callback(struct super_block *sb)
 {
-	struct super_block *sb, *p = NULL;
-
-	spin_lock(&sb_lock);
-	list_for_each_entry(sb, &super_blocks, s_list) {
-		if (hlist_unhashed(&sb->s_instances))
-			continue;
-		sb->s_count++;
-		spin_unlock(&sb_lock);
-		down_write(&sb->s_umount);
-		if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
-		    !sb_rdonly(sb)) {
-			/*
-			 * What lock protects sb->s_flags??
-			 */
-			do_remount_sb(sb, SB_RDONLY, NULL, 1);
-		}
-		up_write(&sb->s_umount);
-		spin_lock(&sb_lock);
-		if (p)
-			__put_super(p);
-		p = sb;
+	down_write(&sb->s_umount);
+	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
+	    !sb_rdonly(sb)) {
+		/*
+		 * What lock protects sb->s_flags??
+		 */
+		do_remount_sb(sb, SB_RDONLY, NULL, 1);
 	}
-	if (p)
-		__put_super(p);
-	spin_unlock(&sb_lock);
+	up_write(&sb->s_umount);
+}
+
+static void do_emergency_remount(struct work_struct *work)
+{
+	__iterate_supers(do_emergency_remount_callback);
 	kfree(work);
 	printk("Emergency Remount complete\n");
 }
@@ -923,6 +944,40 @@ void emergency_remount(void)
 	}
 }
 
+static void do_thaw_all_callback(struct super_block *sb)
+{
+	down_write(&sb->s_umount);
+	if (sb->s_root && sb->s_flags & SB_BORN) {
+		emergency_thaw_bdev(sb);
+		thaw_super_locked(sb);
+	} else {
+		up_write(&sb->s_umount);
+	}
+}
+
+static void do_thaw_all(struct work_struct *work)
+{
+	__iterate_supers(do_thaw_all_callback);
+	kfree(work);
+	printk(KERN_WARNING "Emergency Thaw complete\n");
+}
+
+/**
+ * emergency_thaw_all -- forcibly thaw every frozen filesystem
+ *
+ * Used for emergency unfreeze of all filesystems via SysRq
+ */
+void emergency_thaw_all(void)
+{
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_thaw_all);
+		schedule_work(work);
+	}
+}
+
 /*
  * Unnamed block devices are dummy devices used by virtual
  * filesystems which don't use real block-devices.  -- jrs
@@ -1227,6 +1282,14 @@ mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
 	sb = root->d_sb;
 	BUG_ON(!sb);
 	WARN_ON(!sb->s_bdi);
+
+	/*
+	 * Write barrier is for super_cache_count(). We place it before setting
+	 * SB_BORN as the data dependency between the two functions is the
+	 * superblock structure contents that we just set up, not the SB_BORN
+	 * flag.
+	 */
+	smp_wmb();
 	sb->s_flags |= SB_BORN;
 
 	error = security_sb_kern_mount(sb, flags, secdata);
@@ -1492,11 +1555,10 @@ EXPORT_SYMBOL(freeze_super);
  *
  * Unlocks the filesystem and marks it writeable again after freeze_super().
  */
-int thaw_super(struct super_block *sb)
+static int thaw_super_locked(struct super_block *sb)
 {
 	int error;
 
-	down_write(&sb->s_umount);
 	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
 		up_write(&sb->s_umount);
 		return -EINVAL;
@@ -1527,4 +1589,10 @@ out:
 	deactivate_locked_super(sb);
 	return 0;
 }
+
+int thaw_super(struct super_block *sb)
+{
+	down_write(&sb->s_umount);
+	return thaw_super_locked(sb);
+}
 EXPORT_SYMBOL(thaw_super);