Re: [PATCH] mm/vmscan: Fix a bug calling wakeup_kswapd() with a wrong zone index

[Byungchul Park <byungchul@sk.com>]

On Tue, Feb 20, 2024 at 11:42:31AM +0800, Huang, Ying wrote:
> Byungchul Park <byungchul@sk.com> writes:
> 
> > With numa balancing on, when a numa system is running where a numa node
> > doesn't have its local memory so it has no managed zones, the following
> > oops has been observed. It's because wakeup_kswapd() is called with a
> > wrong zone index, -1. Fixed it by checking the index before calling
> > wakeup_kswapd().
> >
> >> BUG: unable to handle page fault for address: 00000000000033f3
> >> #PF: supervisor read access in kernel mode
> >> #PF: error_code(0x0000) - not-present page
> >> PGD 0 P4D 0
> >> Oops: 0000 [#1] PREEMPT SMP NOPTI
> >> CPU: 2 PID: 895 Comm: masim Not tainted 6.6.0-dirty #255
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> >>    rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> >> RIP: 0010:wakeup_kswapd (./linux/mm/vmscan.c:7812)
> >> Code: (omitted)
> >> RSP: 0000:ffffc90004257d58 EFLAGS: 00010286
> >> RAX: ffffffffffffffff RBX: ffff88883fff0480 RCX: 0000000000000003
> >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88883fff0480
> >> RBP: ffffffffffffffff R08: ff0003ffffffffff R09: ffffffffffffffff
> >> R10: ffff888106c95540 R11: 0000000055555554 R12: 0000000000000003
> >> R13: 0000000000000000 R14: 0000000000000000 R15: ffff88883fff0940
> >> FS:  00007fc4b8124740(0000) GS:ffff888827c00000(0000) knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: 00000000000033f3 CR3: 000000026cc08004 CR4: 0000000000770ee0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> PKRU: 55555554
> >> Call Trace:
> >>  <TASK>
> >> ? __die
> >> ? page_fault_oops
> >> ? __pte_offset_map_lock
> >> ? exc_page_fault
> >> ? asm_exc_page_fault
> >> ? wakeup_kswapd
> >> migrate_misplaced_page
> >> __handle_mm_fault
> >> handle_mm_fault
> >> do_user_addr_fault
> >> exc_page_fault
> >> asm_exc_page_fault
> >> RIP: 0033:0x55b897ba0808
> >> Code: (omitted)
> >> RSP: 002b:00007ffeefa821a0 EFLAGS: 00010287
> >> RAX: 000055b89983acd0 RBX: 00007ffeefa823f8 RCX: 000055b89983acd0
> >> RDX: 00007fc2f8122010 RSI: 0000000000020000 RDI: 000055b89983acd0
> >> RBP: 00007ffeefa821a0 R08: 0000000000000037 R09: 0000000000000075
> >> R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
> >> R13: 00007ffeefa82410 R14: 000055b897ba5dd8 R15: 00007fc4b8340000
> >>  </TASK>
> >
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > Reported-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
> > Cc: stable@vger.kernel.org
> > Fixes: c574bbe917036 ("NUMA balancing: optimize page placement for memory tiering system")
> > ---
> >  mm/migrate.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index fbc8586ed735..51ee6865b0f6 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -2825,6 +2825,14 @@ static int numamigrate_isolate_folio(pg_data_t *pgdat, struct folio *folio)
> >  			if (managed_zone(pgdat->node_zones + z))
> >  				break;
> >  		}
> > +
> > +		/*
> > +		 * If there are no managed zones, it should not proceed
> > +		 * further.
> > +		 */
> > +		if (z < 0)
> > +			return 0;
> > +
> 
> I think that it's better to check pgdat->nr_zones directly earlier in
> the function.  That is a little easier to be understood.

No. No matter what the value of ->nr_zones is, the oops is going to
happen if there are no managed zones by any reason.

	Byungchul

> >  		wakeup_kswapd(pgdat->node_zones + z, 0,
> >  			      folio_order(folio), ZONE_MOVABLE);
> >  		return 0;
> 
> --
> Best Regards,
> Huang, Ying