Re: [PATCH V2] xfs: Fix agi&agf ABBA deadlock when performing rename with RENAME_WHITEOUT flag

[Dave Chinner <david@fromorbit.com>]

On Tue, Aug 20, 2019 at 02:45:36PM +0800, kaixuxia wrote:
> On 2019/8/19 23:13, Brian Foster wrote:
> > 	/* error checks before we dirty the transaction */
> > 	if (!target_ip && !spaceres) {
> > 		error = xfs_dir_canenter();
> > 		...
> > 	} else if (S_ISDIR() && !(empty || nlink > 2))
> > 		error = -EEXIST;
> > 		...
> > 	}
> > 
> > 	if (wip) {
> > 		...
> > 		xfs_iunlink_remove();
> > 	}
> > 
> > 	if (!target_ip) {
> > 		xfs_dir_create();
> > 		...
> > 	} else {
> > 		xfs_dir_replace();
> > 		...
> > 	}
> > 
> > ... but that may not be any cleaner..? It could also be done as a
> > followup cleanup patch as well.
> 
> Yep, it is cleaner that making the whole check before the transaction
> becomes dirty, just return the error code if check failed and
> the filesystem is clean.

*nod*

> Dave gave another solution in the other subthread that using
> XFS_DIR3_FT_WHT, it's a bit more work for this bug, include
> refactoring the xfs_rename() and xfs_lookup(), not sure whether
> it's worth the complex changes for this bug.

It's not necessary to fix the bug, but it's somethign we should
be looking to do because it makes whiteout handling a lot more
efficient - it's just dirent modifications at that point, no inodes
are necessary.

This is how I always intended to handle whiteouts - it's just
another thing on the "we need to fix" list....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com