X-Git-Url: http://git.osdn.net/view?a=blobdiff_plain;f=fs%2Fsuper.c;h=eb27955a229aeef5069b8eb5dfb5cce7b9300ed7;hb=a95e76973d5902f434d6b27345afdd731558df2d;hp=652c9e6b6b9221deabcbe6d131e48fc7d2e2f0b1;hpb=ad09d8c6845e2303b2897b24d385129ab55971b6;p=sagit-ice-cold%2Fkernel_xiaomi_msm8998.git

diff --git a/fs/super.c b/fs/super.c
index 652c9e6b6b92..eb27955a229a 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -118,13 +118,23 @@ 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 MS_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 & MS_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);
 
@@ -1151,6 +1161,14 @@ mount_fs(struct file_system_type *type, int flags, const char *name, struct vfsm
 	sb = root->d_sb;
 	BUG_ON(!sb);
 	WARN_ON(!sb->s_bdi);
+
+	/*
+	 * Write barrier is for super_cache_count(). We place it before setting
+	 * MS_BORN as the data dependency between the two functions is the
+	 * superblock structure contents that we just set up, not the MS_BORN
+	 * flag.
+	 */
+	smp_wmb();
 	sb->s_flags |= MS_BORN;
 
 	error = security_sb_kern_mount(sb, flags, secdata);