[5/6] Btrfs: fix race setting block group back to RW mode during device replace

Commit Message

Filipe Manana May 20, 2016, 4:45 a.m. UTC

From: Filipe Manana <[e-mail]>

After it finishes processing a device extent, the device replace code sets
back the block group to RW mode and then after that it sets the left cursor
to match the logical end address of the block group, so that future writes
into extents belonging to the block group go both the source (old) and
target (new) devices. However from the moment we turn the block group
back to RW mode we have a short time window, that lasts until we update
the left cursor's value, where extents can be allocated from the block
group and written to, in which case they will not be copied/written to
the target (new) device. Fix this by updating the left cursor's value
before turning the block group back to RW mode.

Signed-off-by: Filipe Manana <[e-mail]>
---
 fs/btrfs/scrub.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Comments

Josef Bacik May 20, 2016, 3:22 p.m. UTC | #1

On Fri, May 20, 2016 at 12:45 AM,  <[e-mail]> wrote:
> From: Filipe Manana <[e-mail]>
>
> After it finishes processing a device extent, the device replace code sets
> back the block group to RW mode and then after that it sets the left cursor
> to match the logical end address of the block group, so that future writes
> into extents belonging to the block group go both the source (old) and
> target (new) devices. However from the moment we turn the block group
> back to RW mode we have a short time window, that lasts until we update
> the left cursor's value, where extents can be allocated from the block
> group and written to, in which case they will not be copied/written to
> the target (new) device. Fix this by updating the left cursor's value
> before turning the block group back to RW mode.
>
> Signed-off-by: Filipe Manana <[e-mail]>

Reviewed-by: Josef Bacik <[e-mail]>

Thanks,

Josef
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index a58e0ae..c4c09a8 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3680,6 +3680,11 @@  int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 
 		scrub_pause_off(fs_info);
 
+		btrfs_dev_replace_lock(&fs_info->dev_replace, 1);
+		dev_replace->cursor_left = dev_replace->cursor_right;
+		dev_replace->item_needs_writeback = 1;
+		btrfs_dev_replace_unlock(&fs_info->dev_replace, 1);
+
 		if (ro_set)
 			btrfs_dec_block_group_ro(root, cache);
 
@@ -3717,11 +3722,6 @@  int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 			ret = -ENOMEM;
 			break;
 		}
-
-		btrfs_dev_replace_lock(&fs_info->dev_replace, 1);
-		dev_replace->cursor_left = dev_replace->cursor_right;
-		dev_replace->item_needs_writeback = 1;
-		btrfs_dev_replace_unlock(&fs_info->dev_replace, 1);
 skip:
 		key.offset = found_key.offset + length;
 		btrfs_release_path(path);