On 09/03/2014 09:35 AM, Miao Xie wrote:
> There were several problems about chunk mutex usage:
> - Lock chunk mutex when updating metadata. It would cause the nested
> deadlock because updating metadata might need allocate new chunks
> that need acquire chunk mutex. We remove chunk mutex at this case,
> because b-tree lock and other lock mechanism can help us.
> - ABBA deadlock occured between device_list_mutex and chunk_mutex.
> When we update device status, we must acquire device_list_mutex at the
> beginning, and then we might get chunk_mutex during the device status
> update because we need allocate new chunks for metadata COW. But at
> most place, we acquire chunk_mutex at first and then acquire device list
> mutex. We need change the lock order.
> - Some place we needn't acquire chunk_mutex. For example we needn't get
> chunk_mutex when we free a empty seed fs_devices structure.
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9f22398d..357f911 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
>
> @@ -2619,10 +2615,23 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
> map = (struct map_lookup *)em->bdev;
>
> for (i = 0; i < map->num_stripes; i++) {
> - ret = btrfs_free_dev_extent(trans, map->stripes[i].dev,
> - map->stripes[i].physical);
> + device = map->stripes[i].dev;
> + ret = btrfs_free_dev_extent(trans, device,
> + map->stripes[i].physical,
> + &dev_extent_len);
> BUG_ON(ret);
gcc is worried that dev_extent_len may be used uninitialized here. The
BUG_ON makes it unlikely we'll notice dev_extent_len, but I set it to
zero in my version here.
-chris
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