9 files changed, 197 insertions, 55 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 53af9f5253f4..2cddfe7806a4 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1280,6 +1280,7 @@ struct btrfs_root {
         int send_in_progress;
         struct btrfs_subvolume_writers *subv_writers;
         atomic_t will_be_snapshotted;
+        atomic_t snapshot_force_cow;
 
         /* For qgroup metadata reserved space */
         spinlock_t qgroup_meta_rsv_lock;
@@ -3390,9 +3391,9 @@ do {									\
 #define btrfs_debug(fs_info, fmt, args...) \
         btrfs_no_printk(fs_info, KERN_DEBUG fmt, ##args)
 #define btrfs_debug_in_rcu(fs_info, fmt, args...) \
-        btrfs_no_printk(fs_info, KERN_DEBUG fmt, ##args)
+        btrfs_no_printk_in_rcu(fs_info, KERN_DEBUG fmt, ##args)
 #define btrfs_debug_rl_in_rcu(fs_info, fmt, args...) \
-        btrfs_no_printk(fs_info, KERN_DEBUG fmt, ##args)
+        btrfs_no_printk_in_rcu(fs_info, KERN_DEBUG fmt, ##args)
 #define btrfs_debug_rl(fs_info, fmt, args...) \
         btrfs_no_printk(fs_info, KERN_DEBUG fmt, ##args)
 #endif
@@ -3404,6 +3405,13 @@ do {							\
         rcu_read_unlock();                              \
 } while (0)
 
+#define btrfs_no_printk_in_rcu(fs_info, fmt, args...)   \
+do {                                                    \
+        rcu_read_lock();                                \
+        btrfs_no_printk(fs_info, fmt, ##args);          \
+        rcu_read_unlock();                              \
+} while (0)
+
 #define btrfs_printk_ratelimited(fs_info, fmt, args...)         \
 do {                                                            \
         static DEFINE_RATELIMIT_STATE(_rs,                      \
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5124c15705ce..05dc3c17cb62 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1187,6 +1187,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
         atomic_set(&root->log_batch, 0);
         refcount_set(&root->refs, 1);
         atomic_set(&root->will_be_snapshotted, 0);
+        atomic_set(&root->snapshot_force_cow, 0);
         root->log_transid = 0;
         root->log_transid_committed = -1;
         root->last_log_commit = 0;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index de6f75f5547b..2d9074295d7f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5800,7 +5800,7 @@ void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
  * root: the root of the parent directory
  * rsv: block reservation
  * items: the number of items that we need do reservation
- * qgroup_reserved: used to return the reserved size in qgroup
+ * use_global_rsv: allow fallback to the global block reservation
  *
  * This function is used to reserve the space for snapshot/subvolume
  * creation and deletion. Those operations are different with the
@@ -5810,10 +5810,10 @@ void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
  * the space reservation mechanism in start_transaction().
  */
 int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
-                                     struct btrfs_block_rsv *rsv,
-                                     int items,
+                                     struct btrfs_block_rsv *rsv, int items,
                                      bool use_global_rsv)
 {
+        u64 qgroup_num_bytes = 0;
         u64 num_bytes;
         int ret;
         struct btrfs_fs_info *fs_info = root->fs_info;
@@ -5821,12 +5821,11 @@ int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
 
         if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) {
                 /* One for parent inode, two for dir entries */
-                num_bytes = 3 * fs_info->nodesize;
-                ret = btrfs_qgroup_reserve_meta_prealloc(root, num_bytes, true);
+                qgroup_num_bytes = 3 * fs_info->nodesize;
+                ret = btrfs_qgroup_reserve_meta_prealloc(root,
+                                qgroup_num_bytes, true);
                 if (ret)
                         return ret;
-        } else {
-                num_bytes = 0;
         }
 
         num_bytes = btrfs_calc_trans_metadata_size(fs_info, items);
@@ -5838,8 +5837,8 @@ int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
         if (ret == -ENOSPC && use_global_rsv)
                 ret = btrfs_block_rsv_migrate(global_rsv, rsv, num_bytes, 1);
 
-        if (ret && num_bytes)
-                btrfs_qgroup_free_meta_prealloc(root, num_bytes);
+        if (ret && qgroup_num_bytes)
+                btrfs_qgroup_free_meta_prealloc(root, qgroup_num_bytes);
 
         return ret;
 }
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 9357a19d2bff..3ea5339603cf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1271,7 +1271,7 @@ static noinline int run_delalloc_nocow(struct inode *inode,
         u64 disk_num_bytes;
         u64 ram_bytes;
         int extent_type;
-        int ret, err;
+        int ret;
         int type;
         int nocow;
         int check_prev = 1;
@@ -1403,11 +1403,8 @@ next_slot:
                          * if there are pending snapshots for this root,
                          * we fall into common COW way.
                          */
-                        if (!nolock) {
-                                err = btrfs_start_write_no_snapshotting(root);
-                                if (!err)
-                                        goto out_check;
-                        }
+                        if (!nolock && atomic_read(&root->snapshot_force_cow))
+                                goto out_check;
                         /*
                          * force cow if csum exists in the range.
                          * this ensure that csum for a given extent are
@@ -1416,9 +1413,6 @@ next_slot:
                         ret = csum_exist_in_range(fs_info, disk_bytenr,
                                                   num_bytes);
                         if (ret) {
-                                if (!nolock)
-                                        btrfs_end_write_no_snapshotting(root);
-
                                 /*
                                  * ret could be -EIO if the above fails to read
                                  * metadata.
@@ -1431,11 +1425,8 @@ next_slot:
                                 WARN_ON_ONCE(nolock);
                                 goto out_check;
                         }
-                        if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr)) {
-                                if (!nolock)
-                                        btrfs_end_write_no_snapshotting(root);
+                        if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr))
                                 goto out_check;
-                        }
                         nocow = 1;
                 } else if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                         extent_end = found_key.offset +
@@ -1448,8 +1439,6 @@ next_slot:
 out_check:
                 if (extent_end <= start) {
                         path->slots[0]++;
-                        if (!nolock && nocow)
-                                btrfs_end_write_no_snapshotting(root);
                         if (nocow)
                                 btrfs_dec_nocow_writers(fs_info, disk_bytenr);
                         goto next_slot;
@@ -1471,8 +1460,6 @@ out_check:
                                              end, page_started, nr_written, 1,
                                              NULL);
                         if (ret) {
-                                if (!nolock && nocow)
-                                        btrfs_end_write_no_snapshotting(root);
                                 if (nocow)