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SubjectRe: [Ocfs2-devel] [PATCH] fix dead lock caused by ocfs2_defrag_extent
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Hi Larry,

On 18/8/27 16:01, Larry Chen wrote:
> ocfs2_defrag_extent may fall into dead lock.
>
> ocfs2_ioctl_move_extents
> ocfs2_ioctl_move_extents
> ocfs2_move_extents
> ocfs2_defrag_extent
> ocfs2_lock_allocators_move_extents
>
> ocfs2_reserve_clusters
> inode_lock GLOBAL_BITMAP_SYSTEM_INODE
>
> __ocfs2_flush_truncate_log
> inode_lock GLOBAL_BITMAP_SYSTEM_INODE
>
> As back trace shows above, ocfs2_reserve_clusters will call inode_lock
> against the global bitmap if local allocator has not sufficient cluters.
> Once global bitmap could meet the demand, ocfs2_reserve_cluster will
> return success with global bitmap locked.
>
> After ocfs2_reserve_cluster, if truncate log is full,
> __ocfs2_flush_truncate_log will definitely fall into dead lock
> because it needs to inode_lock global bitmap, which has
> already been locked.
>
> To fix this bug, we could remove from ocfs2_lock_allocators_move_extents
> the code which intends to lock global allocator, and put the removed
> code after __ocfs2_flush_truncate_log
>
> The ocfs2_lock_allocators_move_extents has been refered by 2 places, one
> is here, the other does not need the data allocator context, which means
> this patch does not affect the caller so far.
>
After this change, data_ac in ocfs2_lock_allocators_move_extents() is
no longer used. So I'd prefer we also clean it up.

Thanks,
Joseph

>
>
> Signed-off-by: Larry Chen <lchen@suse.com>
> ---
> fs/ocfs2/move_extents.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
> index 7eb3b0a6347e..064dedf40d74 100644
> --- a/fs/ocfs2/move_extents.c
> +++ b/fs/ocfs2/move_extents.c
> @@ -192,13 +192,6 @@ static int ocfs2_lock_allocators_move_extents(struct inode *inode,
> goto out;
> }
>
> - if (data_ac) {
> - ret = ocfs2_reserve_clusters(osb, clusters_to_move, data_ac);
> - if (ret) {
> - mlog_errno(ret);
> - goto out;
> - }
> - }
>
> *credits += ocfs2_calc_extend_credits(osb->sb, et->et_root_el);
>
> @@ -283,6 +276,12 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context,
> }
> }
>
> + ret = ocfs2_reserve_clusters(osb, *len, &context->data_ac);
> + if (ret) {
> + mlog_errno(ret);
> + goto out_unlock_mutex;
> + }
> +
> handle = ocfs2_start_trans(osb, credits);
> if (IS_ERR(handle)) {
> ret = PTR_ERR(handle);
>

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