Re: [PATCH 2/2] xfs: fix double ijoin in xfs_reflink_cancel_cow_range

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Mar 07, 2018 at 08:10:20PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> AN inode is joined to teh same transaction twice in
> xfs_reflink_cancel_cow_range() resulting in the following assert
> failure:
> 
> [   30.180485] XFS: Assertion failed: !(lip->li_flags & XFS_LI_TRANS), file: fs/xfs/xfs_trans.c, line: 740
> [   30.183435] ------------[ cut here ]------------
> ......
> [   30.209264] Call Trace:
> [   30.209935]  xfs_trans_add_item+0xcc/0xe0
> [   30.210968]  xfs_reflink_cancel_cow_blocks+0xab/0x290
> [   30.212249]  ? xfs_trans_reserve+0x1b4/0x2b0
> [   30.213320]  ? kmem_zone_alloc+0x61/0xe0
> [   30.214321]  xfs_reflink_cancel_cow_range+0xb2/0x1f0
> [   30.215616]  xfs_fs_destroy_inode+0x1bd/0x280
> [   30.216757]  dispose_list+0x35/0x40
> [   30.217656]  evict_inodes+0x132/0x160
> [   30.218620]  generic_shutdown_super+0x3a/0x110
> [   30.219771]  kill_block_super+0x21/0x50
> [   30.220762]  deactivate_locked_super+0x39/0x70
> [   30.221909]  cleanup_mnt+0x3b/0x70
> [   30.222819]  task_work_run+0x7f/0xa0
> [   30.223762]  exit_to_usermode_loop+0x9b/0xa0
> [   30.224884]  do_syscall_64+0x18f/0x1a0
> 
> Fix it and document that the callers of
> xfs_reflink_cancel_cow_blocks() must have already joined the inode
> to the permanent transaction passed in.
> 
> Signed-Off-By: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_reflink.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 8c16177b33d4..6225d1ea3fdb 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -552,6 +552,9 @@ xfs_reflink_trim_irec_to_next_cow(
>   *
>   * If cancel_real is true this function cancels all COW fork extents for the
>   * inode; if cancel_real is false, real extents are not cleared.
> + *
> + * Caller must have already joined the inode to the current transaction. The
> + * inode will be joined to the transaction returned to the caller.
>   */
>  int
>  xfs_reflink_cancel_cow_blocks(
> @@ -592,7 +595,6 @@ xfs_reflink_cancel_cow_blocks(
>  			if (error)
>  				break;
>  		} else if (del.br_state == XFS_EXT_UNWRITTEN || cancel_real) {
> -			xfs_trans_ijoin(*tpp, ip, 0);

Looks ok, but...

>  			xfs_defer_init(&dfops, &firstfsb);
>  
>  			/* Free the CoW orphan record. */
> @@ -1571,6 +1573,7 @@ xfs_reflink_clear_inode_flag(

Wait, what?  Why are we messing with xfs_reflink_clear_inode_flag here?

(Shame on me for looking at patch 3 before patch 2.)

The comment update in patch 3 is fine (caller must ijoin, function will
ijoin if returning new transaction) but ... didn't this function already
do all this before this churn below?

--D

>  	 * We didn't find any shared blocks so turn off the reflink flag.
>  	 * First, get rid of any leftover CoW mappings.
>  	 */
> +	xfs_trans_ijoin(*tpp, ip, 0);
>  	error = xfs_reflink_cancel_cow_blocks(ip, tpp, 0, NULLFILEOFF, true);
>  	if (error)
>  		return error;
> @@ -1579,7 +1582,6 @@ xfs_reflink_clear_inode_flag(
>  	trace_xfs_reflink_unset_inode_flag(ip);
>  	ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
>  	xfs_inode_clear_cowblocks_tag(ip);
> -	xfs_trans_ijoin(*tpp, ip, 0);
>  	xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);
>  
>  	return error;
> -- 
> 2.16.1
> 
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