Re: [BISECTED] first bad commit is c203c6d5b3f0597 ("migrate_pages: batch _unmap and _move")

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

On Fri, Feb 03, 2023 at 07:17:14AM +0800, Huang, Ying wrote:
> "Huang, Ying" <ying.huang@intel.com> writes:
> 
> > Hi, Hyeonggon,
> >
> > Hyeonggon Yoo <42.hyeyoo@gmail.com> writes:
> >
> >> On Wed, Feb 01, 2023 at 01:09:10AM +0900, Hyeonggon Yoo wrote:
> >>> I've observed random list_del corruption on mm-unstable,
> >>> where HEAD is commit d69862e693c069f4
> >>> ("mm/migrate: convert putback_movable_pages() to use folios").
> >>> 
> >>> The issue can be easily reproduced by stressing MM multiple times:
> >>> 	stress-ng --bigheap 0 --timeout 300
> >>> 
> >>> The compiler is gcc 12.2.1 and config, dmesg are included as attachment.
> >>> I will try to bisect but can't promise quick resolution :)
> >>
> >>
> >> The first bad commits appears to be:
> >> c203c6d5b3f0597 ("migrate_pages: batch _unmap and _move")
> >>
> >> the first bad commit _probably_ be earlier, but this is quite
> >> easy to reproduce so at this point I think above is the real bad commit.
> >
> > Thank you very much for reporting the bug.  I'm in travel now but I will
> > try to find some time to reproduce and debug it.
> 
> Still haven't reproduced the issue.  But after reviewing the code, I
> found a bug in the code, which may cause list corruption.  Can you try
> the debug patch below?

Unfortunately my home server seems to be broken again :(
That means I only have access to VMs and not a real machine now.

FYI it was not reproduced on KVM but reproduced on real machine.
Could you try checking on your machine with the config I attached? [1]

Sorry to bother your travel!

[1] https://marc.info/?l=linux-mm&m=167518135116956

Thanks,
Hyeonggon

> Best Regards,
> Huang, Ying
> 
> -------------------------------8<-------------------------------------
> From a4eef847fe4f6e50b6c3f69651c1dfdeb4b23bc4 Mon Sep 17 00:00:00 2001
> From: Huang Ying <ying.huang@intel.com>
> Date: Fri, 3 Feb 2023 07:12:24 +0800
> Subject: [PATCH] dbg: fix list corruption for -EAGAIN
> 
> ---
>  mm/migrate.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 143d96775b4d..4205a0297ef8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1230,11 +1230,11 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,
>  
>  	rc = move_to_new_folio(dst, src, mode);
>  
> -	if (rc != -EAGAIN)
> +	if (rc != -EAGAIN) {
>  		list_del(&dst->lru);
> -
> -	if (unlikely(!is_lru))
> -		goto out_unlock_both;
> +		if (unlikely(!is_lru))
> +			goto out_unlock_both;
> +	}
>  
>  	/*
>  	 * When successful, push dst to LRU immediately: so that if it
> -- 
> 2.35.1
>