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[v4,1/3] btrfs: Fix lost-data-profile caused by auto removing bg

Message ID 3b7959e1293407ddf7ffe7c6ac2fe08197b93916.1444301652.git.zhaolei@cn.fujitsu.com (mailing list archive)
State Accepted
Headers show

Commit Message

Zhaolei Oct. 8, 2015, 10:59 a.m. UTC
Reproduce:
 (In integration-4.3 branch)

 TEST_DEV=(/dev/vdg /dev/vdh)
 TEST_DIR=/mnt/tmp

 umount "$TEST_DEV" >/dev/null
 mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"

 mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
 umount "$TEST_DEV"

 mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
 btrfs filesystem usage $TEST_DIR

We can see the data chunk changed from raid1 to single:
 # btrfs filesystem usage $TEST_DIR
 Data,single: Size:8.00MiB, Used:0.00B
    /dev/vdg        8.00MiB
 #

Reason:
 When a empty filesystem mount with -o nospace_cache, the last
 data blockgroup will be auto-removed in umount.

 Then if we mount it again, there is no data chunk in the
 filesystem, so the only available data profile is 0x0, result
 is all new chunks are created as single type.

Fix:
 Don't auto-delete last blockgroup for a raid type.

Test:
 Test by above script, and confirmed the logic by debug output.

Changelog v3->v4:
1: Avoid down_read() in spin_lock context.
   Noticed-by: Chris Mason <clm@fb.com>

Changelog v2->v3:
1: Use list_is_singular() instead of
   block_group->list.next == block_group->list.prev
   Suggested-by: Jeff Mahoney <jeffm@suse.com>

Changelog v1->v2:
1: Put code of checking block_group->list into
   semaphore of space_info->groups_sem.
   Noticed-by: Filipe Manana <fdmanana@gmail.com>

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/extent-tree.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
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Patch

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 79a5bd9..00c621b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10010,8 +10010,10 @@  void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		block_group = list_first_entry(&fs_info->unused_bgs,
 					       struct btrfs_block_group_cache,
 					       bg_list);
-		space_info = block_group->space_info;
 		list_del_init(&block_group->bg_list);
+
+		space_info = block_group->space_info;
+
 		if (ret || btrfs_mixed_space_info(space_info)) {
 			btrfs_put_block_group(block_group);
 			continue;
@@ -10025,7 +10027,8 @@  void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		spin_lock(&block_group->lock);
 		if (block_group->reserved ||
 		    btrfs_block_group_used(&block_group->item) ||
-		    block_group->ro) {
+		    block_group->ro ||
+		    list_is_singular(&block_group->list)) {
 			/*
 			 * We want to bail if we made new allocations or have
 			 * outstanding allocations in this block group.  We do