linux-kernel - Re: [PATCH] xfs: Use for_each_perag() to iterate all available AGs

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Date:   Wed, 5 Apr 2023 11:04:03 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Ryosuke Yasuoka <ryasuoka@...hat.com>
Cc:     djwong@...nel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: Use for_each_perag() to iterate all available AGs

On Tue, Apr 04, 2023 at 05:47:01PM +0900, Ryosuke Yasuoka wrote:
> for_each_perag_wrap() doesn't expect 0 as 2nd arg.
> To iterate all the available AGs, just use for_each_perag() instead.

Thanks, Ryosuke-san. IIUC, this is a fix for the recent sysbot
reported filestreams oops regression?

Can you include the context of the failure it reported (i.e. the
trace from the oops), and the 'reported-by' tag for the syzbot
report?

It should probably also include a 'Fixes: bd4f5d09cc93 ("xfs:
refactor the filestreams allocator pick functions")' tag as well.

> Signed-off-by: Ryosuke Yasuoka <ryasuoka@...hat.com>
> ---
>  fs/xfs/xfs_filestream.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
> index 22c13933c8f8..48f43c340c58 100644
> --- a/fs/xfs/xfs_filestream.c
> +++ b/fs/xfs/xfs_filestream.c
> @@ -151,7 +151,7 @@ xfs_filestream_pick_ag(
>  		 * grab.
>  		 */
>  		if (!max_pag) {
> -			for_each_perag_wrap(args->mp, 0, start_agno, args->pag)
> +			for_each_perag(args->mp, start_agno, args->pag)
>  				break;

While this will definitely avoid the oops, I don't think it is quite
right. If we want to iterate all AGs, then we should be starting the
iteration at AG 0, not start_agno. i.e.

+			for_each_perag(args->mp, 0, args->pag)

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com