From: Robbie Ko <robbieko@xxxxxxxxxxxx>
When creating a snapshot, it takes a long time because
flush dirty data is required.
But we have taken two resources as shown below:
1. Destination directory inode lock
2. Global subvol semaphore
This will cause subvol destroy/create/setflag blocked,
until the snapshot is created.
We fix by flush dirty data first to reduce the time of
the critical section, and then lock the relevant resources.
Signed-off-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
---
fs/btrfs/ioctl.c | 70 ++++++++++++++++++++++++++++--------------------
1 file changed, 41 insertions(+), 29 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 40b729dce91c..d0c1598dc51e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -748,7 +748,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
struct btrfs_pending_snapshot *pending_snapshot;
struct btrfs_trans_handle *trans;
int ret;
- bool snapshot_force_cow = false;
if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
return -EINVAL;
@@ -771,27 +770,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
goto free_pending;
}
- /*
- * Force new buffered writes to reserve space even when NOCOW is
- * possible. This is to avoid later writeback (running dealloc) to
- * fallback to COW mode and unexpectedly fail with ENOSPC.
- */
- btrfs_drew_read_lock(&root->snapshot_lock);
-
- ret = btrfs_start_delalloc_snapshot(root);
- if (ret)
- goto dec_and_free;
-
- /*
- * All previous writes have started writeback in NOCOW mode, so now
- * we force future writes to fallback to COW mode during snapshot
- * creation.
- */
- atomic_inc(&root->snapshot_force_cow);
- snapshot_force_cow = true;
-
- btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
-
btrfs_init_block_rsv(&pending_snapshot->block_rsv,
BTRFS_BLOCK_RSV_TEMP);
/*
@@ -806,7 +784,7 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
&pending_snapshot->block_rsv, 8,
false);
if (ret)
- goto dec_and_free;
+ goto free_pending;
pending_snapshot->dentry = dentry;
pending_snapshot->root = root;
@@ -848,11 +826,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
fail:
btrfs_put_root(pending_snapshot->snap);
btrfs_subvolume_release_metadata(fs_info, &pending_snapshot->block_rsv);
-dec_and_free:
- if (snapshot_force_cow)
- atomic_dec(&root->snapshot_force_cow);
- btrfs_drew_read_unlock(&root->snapshot_lock);
-
free_pending:
kfree(pending_snapshot->root_item);
btrfs_free_path(pending_snapshot->path);
@@ -983,6 +956,45 @@ static noinline int btrfs_mksubvol(const struct path *parent,
return error;
}
+static noinline int btrfs_mksnapshot(const struct path *parent,
+ const char *name, int namelen,
+ struct btrfs_root *root,
+ bool readonly,
+ struct btrfs_qgroup_inherit *inherit)
+{
+ int ret;
+ bool snapshot_force_cow = false;
+
+ /*
+ * Force new buffered writes to reserve space even when NOCOW is
+ * possible. This is to avoid later writeback (running dealloc) to
+ * fallback to COW mode and unexpectedly fail with ENOSPC.
+ */
+ btrfs_drew_read_lock(&root->snapshot_lock);
+
+ ret = btrfs_start_delalloc_snapshot(root);
+ if (ret)
+ goto out;
+
+ /*
+ * All previous writes have started writeback in NOCOW mode, so now
+ * we force future writes to fallback to COW mode during snapshot
+ * creation.
+ */
+ atomic_inc(&root->snapshot_force_cow);
+ snapshot_force_cow = true;
+
+ btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
+
+ ret = btrfs_mksubvol(parent, name, namelen,
+ root, readonly, inherit);
+out:
+ if (snapshot_force_cow)
+ atomic_dec(&root->snapshot_force_cow);
+ btrfs_drew_read_unlock(&root->snapshot_lock);
+ return ret;
+}
+
/*
* When we're defragging a range, we don't want to kick it off again
* if it is really just waiting for delalloc to send it down.
@@ -1762,7 +1774,7 @@ static noinline int __btrfs_ioctl_snap_create(struct file *file,
*/
ret = -EPERM;
} else {
- ret = btrfs_mksubvol(&file->f_path, name, namelen,
+ ret = btrfs_mksnapshot(&file->f_path, name, namelen,
BTRFS_I(src_inode)->root,
readonly, inherit);
}
--
2.17.1
