Re: [Ocfs2-devel] [PATCH V2] ocfs2: fix dead lock caused by ocfs2_defrag_extent

[Changwei Ge]

Hi Larry,

I still have a few tiny comments for your patch, please refer to them.

On 2018/11/1 5:28, Andrew Morton wrote:
> 
> Folks, could we please review this patch for upstream inclusion?
> 
> Thanks.
> 
> 
> From: Larry Chen <lchen@xxxxxxxx>
> Subject: ocfs2: fix deadlock caused by ocfs2_defrag_extent
> 
> ocfs2_defrag_extent may fall into deadlock.
> 
> 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 backtrace 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 deadlock 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().
> 
> ocfs2_lock_allocators_move_extents() is 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.
> 
> [lchen@xxxxxxxx: rename ocfs2_lock_allocators_move_extents() to ocfs2_lock_meta_allocator_move_extents(), add some comments]
>    Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_20180902091455.23862-2D1-2Dlchen-40suse.com&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=C7gAd4uDxlAvTdc0vmU6X8CMk6L2iDY8-HD0qT6Fo7Y&m=K8aRgOiMescamJW-IuHq-cW4mWedGQv2JTT-2KPy1RI&s=3fQHFtwgixirPeQ5Px4fRBnd_UcSx3rvSsLKLidwESo&e=
> Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_20180827080121.31145-2D1-2Dlchen-40suse.com&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=C7gAd4uDxlAvTdc0vmU6X8CMk6L2iDY8-HD0qT6Fo7Y&m=K8aRgOiMescamJW-IuHq-cW4mWedGQv2JTT-2KPy1RI&s=PQOJREyeElsg_1IlINdSGefNqA6w_cUrI1ezdVxyi7o&e=
> Signed-off-by: Larry Chen <lchen@xxxxxxxx>
> Cc: Mark Fasheh <mark@xxxxxxxxxx>
> Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
> Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> Cc: Joseph Qi <jiangqi903@xxxxxxxxx>
> Cc: Changwei Ge <ge.changwei@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>   fs/ocfs2/move_extents.c |   40 +++++++++++++++++++++++---------------
>   1 file changed, 25 insertions(+), 15 deletions(-)
> 
> --- a/fs/ocfs2/move_extents.c~fix-dead-lock-caused-by-ocfs2_defrag_extent
> +++ a/fs/ocfs2/move_extents.c
> @@ -162,7 +162,7 @@ out:
>    * in some cases, we don't need to reserve clusters, just let data_ac
>    * be NULL.
>    */
> -static int ocfs2_lock_allocators_move_extents(struct inode *inode,
> +static int ocfs2_lock_meta_allocator_move_extents(struct inode *inode,
>   					struct ocfs2_extent_tree *et,
>   					u32 clusters_to_move,
>   					u32 extents_to_split,

After removing 'reserving clusters logic' out of this function, I suggest to also change the function header comments.
And I think there is no need for arguments _data_ac_ now.
Otherwise this patch looks sane to me.

Thanks,
Changwei

> @@ -192,13 +192,6 @@ static int ocfs2_lock_allocators_move_ex
>   		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);
>   
> @@ -257,10 +250,11 @@ static int ocfs2_defrag_extent(struct oc
>   		}
>   	}
>   
> -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, *len, 1,
> -						 &context->meta_ac,
> -						 &context->data_ac,
> -						 extra_blocks, &credits);
> +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
> +						*len, 1,
> +						&context->meta_ac,
> +						&context->data_ac,
> +						extra_blocks, &credits);
>   	if (ret) {
>   		mlog_errno(ret);
>   		goto out;
> @@ -283,6 +277,21 @@ static int ocfs2_defrag_extent(struct oc
>   		}
>   	}
>   
> +	/*
> +	 * Make sure ocfs2_reserve_cluster is called after
> +	 * __ocfs2_flush_truncate_log, otherwise, dead lock may happen.
> +	 *
> +	 * If ocfs2_reserve_cluster is called
> +	 * before __ocfs2_flush_truncate_log, dead lock on global bitmap
> +	 * may happen.
> +	 *
> +	 */
> +	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);
> @@ -600,9 +609,10 @@ static int ocfs2_move_extent(struct ocfs
>   		}
>   	}
>   
> -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, len, 1,
> -						 &context->meta_ac,
> -						 NULL, extra_blocks, &credits);
> +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
> +						len, 1,
> +						&context->meta_ac,
> +						NULL, extra_blocks, &credits);
>   	if (ret) {
>   		mlog_errno(ret);
>   		goto out;
> _
> 
> 
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