On Fri, Nov 13, 2009 at 8:06 PM, Josef Bacik <josef@xxxxxxxxxx> wrote:
> We can race with the unmount of an fs and the stopping of a kthread where we
> will free the block group before we're done using it. The reason for this is
> because we do not hold a reference on the block group while its caching, since
> the allocator drops its reference once it exits or moves on to the next block
> group. This patch fixes the problem by taking a reference to the block group
> before we start caching and dropping it when we're done to make sure all
> accesses to the block group are safe. Thanks,
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 2a4cdce..197bc1b 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -399,6 +399,8 @@ err:
>
> put_caching_control(caching_ctl);
> atomic_dec(&block_group->space_info->caching_threads);
> + btrfs_put_block_group(block_group);
> +
> return 0;
> }
>
> @@ -439,6 +441,7 @@ static int cache_block_group(struct btrfs_block_group_cache *cache)
> up_write(&fs_info->extent_commit_sem);
>
> atomic_inc(&cache->space_info->caching_threads);
> + atomic_inc(&cache->count);
It would be slightly more informative/stylish if
atomic_inc(&cache->count) is replaced by a cal to
static inline void btrfs_get_block_group(struct btrfs_block_group_cache *cache)
{
atomic_inc(&cache->count);
}
Regards,
Andrey
>
> tsk = kthread_run(caching_kthread, cache, "btrfs-cache-%llu\n",
> cache->key.objectid);
> --
> 1.5.4.3
>
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