Btrfs: use a lock to protect incompat/compat flag of the super block

The following case will make the incompat/compat flag of the super block
be recovered.
 Task1					|Task2
 flags = btrfs_super_incompat_flags();	|
					|flags = btrfs_super_incompat_flags();
 flags |= new_flag1;			|
					|flags |= new_flag2;
 btrfs_set_super_incompat_flags(flags);	|
					|btrfs_set_super_incompat_flags(flags);
the new_flag1 is recovered.

In order to avoid this problem, we introduce a lock named super_lock into
the btrfs_fs_info structure. If we want to update incompat/compat flags
of the super block, we must hold it.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

3 files changed, 26 insertions, 11 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1a850402937d..c3b15f8dca00 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1362,6 +1362,17 @@ struct btrfs_fs_info {
         wait_queue_head_t transaction_blocked_wait;
         wait_queue_head_t async_submit_wait;
 
+        /*
+         * Used to protect the incompat_flags, compat_flags, compat_ro_flags
+         * when they are updated.
+         *
+         * Because we do not clear the flags for ever, so we needn't use
+         * the lock on the read side.
+         *
+         * We also needn't use the lock when we mount the fs, because
+         * there is no other task which will update the flag.
+         */
+        spinlock_t super_lock;
         struct btrfs_super_block *super_copy;
         struct btrfs_super_block *super_for_commit;
         struct block_device *__bdev;
@@ -3688,8 +3699,15 @@ static inline void __btrfs_set_fs_incompat(struct btrfs_fs_info *fs_info,
         disk_super = fs_info->super_copy;
         features = btrfs_super_incompat_flags(disk_super);
         if (!(features & flag)) {
-                features |= flag;
-                btrfs_set_super_incompat_flags(disk_super, features);
+                spin_lock(&fs_info->super_lock);
+                features = btrfs_super_incompat_flags(disk_super);
+                if (!(features & flag)) {
+                        features |= flag;
+                        btrfs_set_super_incompat_flags(disk_super, features);
+                        printk(KERN_INFO "btrfs: setting %llu feature flag\n",
+                                         flag);
+                }
+                spin_unlock(&fs_info->super_lock);
         }
 }
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9f83e5b870d2..8a7a366267ec 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2086,6 +2086,7 @@ int open_ctree(struct super_block *sb,
         spin_lock_init(&fs_info->defrag_inodes_lock);
         spin_lock_init(&fs_info->free_chunk_lock);
         spin_lock_init(&fs_info->tree_mod_seq_lock);
+        spin_lock_init(&fs_info->super_lock);
         rwlock_init(&fs_info->tree_mod_log_lock);
         mutex_init(&fs_info->reloc_mutex);
         seqlock_init(&fs_info->profiles_lock);
@@ -2349,6 +2350,10 @@ int open_ctree(struct super_block *sb,
                 goto fail_alloc;
         }
 
+        /*
+         * Needn't use the lock because there is no other task which will
+         * update the flag.
+         */
         btrfs_set_super_incompat_flags(disk_super, features);
 
         features = btrfs_super_compat_ro_flags(disk_super) &
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5aa52ee5c25e..76ded9eb77a7 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3674,18 +3674,10 @@ static u32 find_raid56_stripe_len(u32 data_devices, u32 dev_stripe_target)
 
 static void check_raid56_incompat_flag(struct btrfs_fs_info *info, u64 type)
 {
-        u64 features;
-
         if (!(type & (BTRFS_BLOCK_GROUP_RAID5 | BTRFS_BLOCK_GROUP_RAID6)))
                 return;
 
-        features = btrfs_super_incompat_flags(info->super_copy);
-        if (features & BTRFS_FEATURE_INCOMPAT_RAID56)
-                return;
-
-        features |= BTRFS_FEATURE_INCOMPAT_RAID56;
-        btrfs_set_super_incompat_flags(info->super_copy, features);
-        printk(KERN_INFO "btrfs: setting RAID5/6 feature flag\n");
+        btrfs_set_fs_incompat(info, RAID56);
 }
 
 static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,