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

[Byungchul Park <byungchul@sk.com>]

On Mon, Feb 19, 2024 at 02:25:11PM +0800, Baolin Wang wrote:
> 
> 
> On 2024/2/16 19:15, Byungchul Park wrote:
> > 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")
> 
> This means that there is no memory on the target node？ if so, we can add a
> check at the beginning to avoid calling unnecessary
> migrate_misplaced_folio().

Right. However, the check is necessary no matter where it comes from.
FYI, the fix is going on in another thread:

https://lore.kernel.org/lkml/20240216114045.24828-1-byungchul@sk.com/
https://lore.kernel.org/lkml/20240219041920.1183-1-byungchul@sk.com/

	Byungchul

> diff --git a/mm/memory.c b/mm/memory.c
> index e95503d7544e..a64a1aac463f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5182,7 +5182,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
>         else
>                 last_cpupid = folio_last_cpupid(folio);
>         target_nid = numa_migrate_prep(folio, vma, vmf->address, nid,
> &flags);
> -       if (target_nid == NUMA_NO_NODE) {
> +       if (target_nid == NUMA_NO_NODE || !node_state(target_nid, N_MEMORY))
> {
>                 folio_put(folio);
>                 goto out_map;
>         }
> 
> (similar changes for do_huge_pmd_numa_page())
> 
> > ---
> >   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;
> > +
> >   		wakeup_kswapd(pgdat->node_zones + z, 0,
> >   			      folio_order(folio), ZONE_MOVABLE);
> >   		return 0;