Re: Fwd: crash/hang in mm/swapfile.c:718 add_to_avail_list when exercising stress-ng

[Lu, Aaron]

On Thu, 2023-08-03 at 23:04 +0800, Kefeng Wang wrote:
> 
> On 2023/8/3 21:41, Aaron Lu wrote:
> > On Thu, Aug 03, 2023 at 02:06:46PM +0800, Aaron Lu wrote:
> > > On Wed, Aug 02, 2023 at 07:54:38PM +0700, Bagas Sanjaya wrote:
> > > > Hi,
> > > > 
> > > > I notice a bug report on Bugzilla [1]. Quoting from it:
> > > > 
> > > > > How to reproduce:
> > > > > 
> > > > > Had 24 CPU Alderlake 16GB debian12 system running with default kernel (from makecondig) on 6.5-rc4, exercised with no swap to start with.
> > > > > 
> > > > > using stress-ng tip commit 0f2ef02e9bc5abb3419c44be056d5fa3c97e0137
> > > > > (see https://github.com/ColinIanKing/stress-ng )
> > > > > 
> > > > > build and run stress-ng for say 60 minutes:
> > > > > 
> > > > > ./stress-ng --cpu-online 50 --brk 50 --swap 50 --vmstat 1 -t 60m
> > > > > 
> > > > > Will hang in mm/swapfile.c:718 add_to_avail_list+0x93/0xa0
> > > > > 
> > > > > See attached file for an image of the console on the hang (I'm trying to get the full stack dump).
> > > > 
> > > > See Bugzilla for the full thread and attached console image.
> > > > 
> > > > FWIW, I have to forward this bug report to the mailing lists because
> > > > Thorsten noted that many developers don't take a look on Bugzilla
> > > > (see the BZ thread).
> > > 
> > > Thanks.
> > > 
> > > I can reproduce this issue using below cmdline:
> > > $ sudo ./stress-ng --brk 50 --swap 5 --vmstat 1 -t 60m
> > > 
> > > I'll investigate what is happening.
> > 
> > Hi Colin,
> > 
> > Can you try the below diff on top of v6.5-rc4? It works for me here
> > although I got the warn in a different place in get_swap_pages():
> > 
> >                          WARN(!si->highest_bit,
> >                               "swap_info %d in list but !highest_bit\n",
> >                               si->type);
> > 
> > I think the warn you got in add_to_avail_list() due to the swap device
> > is already in the list is similar, see below explanation.
> > 
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 8e6dde68b389..cb7e93ec1933 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -2330,7 +2330,8 @@ static void _enable_swap_info(struct swap_info_struct *p)
> >   	 * swap_info_struct.
> >   	 */
> >   	plist_add(&p->list, &swap_active_head);
> > -	add_to_avail_list(p);
> > +	if (p->highest_bit)
> > +		add_to_avail_list(p);
> >   }
> 
> There is a patch in next,
> 
> commit bdfc7028681ddbce5ab08f4888d157a981060544
> Author: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> Date:   Tue Jun 27 20:08:33 2023 +0800
> 
>      swap: stop add to avail list if swap is full
> 

Ah, should have tried mm-unstable first.

I took a look at that commit and it's exact the same issue and same fix
so with that fix, we are good now.

> 
> 
> >   
> >   static void enable_swap_info(struct swap_info_struct *p, int prio,
> > 
> > The finding is, if a swap device failed to be swapoff, then it will be
> > reinsert_swap_info() -> _enable_swap_info() -> add_to_avail_list(). The
> > problem is, this swap device may run out of space with its highest_bit
> > being 0 and shouldn't be added to avail list. In your case, once its
> > highest_bit becomes non-zero, it will go through add_to_avail_list()
> > and since it's already in the list, thus the warn.
> > 
> > If it works for you, I'll prepare a patch. Thanks.
> >