Re: [PATCH] xfs: eliminate lockdep false positives in xfs_attr_shortform_list

["Darrick J. Wong" <djwong@kernel.org>]

On Sat, Jun 22, 2024 at 04:26:31PM +0800, Long Li wrote:
> xfs_attr_shortform_list() only called from a non-transactional context, it
> hold ilock before alloc memory and maybe trapped in memory reclaim. Since
> commit 204fae32d5f7("xfs: clean up remaining GFP_NOFS users") removed
> GFP_NOFS flag, lockdep warning will be report as [1]. Eliminate lockdep
> false positives by use __GFP_NOLOCKDEP to alloc memory
> in xfs_attr_shortform_list().
> 
> [1] https://lore.kernel.org/linux-xfs/000000000000e33add0616358204@google.com/
> Reported-by: syzbot+4248e91deb3db78358a2@syzkaller.appspotmail.com
> Signed-off-by: Long Li <leo.lilong@huawei.com>
> ---
>  fs/xfs/xfs_attr_list.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_attr_list.c b/fs/xfs/xfs_attr_list.c
> index 5c947e5ce8b8..8cd6088e6190 100644
> --- a/fs/xfs/xfs_attr_list.c
> +++ b/fs/xfs/xfs_attr_list.c
> @@ -114,7 +114,8 @@ xfs_attr_shortform_list(
>  	 * It didn't all fit, so we have to sort everything on hashval.
>  	 */
>  	sbsize = sf->count * sizeof(*sbuf);
> -	sbp = sbuf = kmalloc(sbsize, GFP_KERNEL | __GFP_NOFAIL);
> +	sbp = sbuf = kmalloc(sbsize,
> +			GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);

Why wouldn't we memalloc_nofs_save any time we take an ILOCK when we're
not in transaction context?  Surely you'd want to NOFS /any/ allocation
when the ILOCK is held, right?

--D

>  
>  	/*
>  	 * Scan the attribute list for the rest of the entries, storing
> -- 
> 2.39.2
> 
>