[PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

While running qemu with a configuration where some CPUs don't have their
local memory and with a kernel numa balancing on, the following oops has
been observed. It's because of null pointers of ->zone_pgdat of zones of
those nodes that are not initialized at booting time. So should avoid
nodes not set N_MEMORY from getting promoted.

> 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>
> Modules linked in:
> CR2: 00000000000033f3
> ---[ end trace 0000000000000000  ]---
> 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
> note: masim[895] exited with irqs disabled

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reported-by: hyeongtak.ji@sk.com
---
 kernel/sched/fair.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d7a3c63a2171..6d215cc85f14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1828,6 +1828,23 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 	int dst_nid = cpu_to_node(dst_cpu);
 	int last_cpupid, this_cpupid;
 
+	/*
+	 * A node of dst_nid might not have its local memory. Promoting
+	 * a folio to the node is meaningless. What's even worse, oops
+	 * can be observed by the null pointer of ->zone_pgdat in
+	 * various points of the code during migration.
+	 *
+	 * For instance, oops has been observed at CPU2 while qemu'ing:
+	 *
+	 * {qemu} \
+	 *    -numa node,nodeid=0,mem=1G,cpus=0-1 \
+	 *    -numa node,nodeid=1,cpus=2-3 \
+	 *    -numa node,nodeid=2,mem=8G \
+	 *    ...
+	 */
+	if (!node_state(dst_nid, N_MEMORY))
+		return false;
+
 	/*
 	 * The pages in slow memory node should be migrated according
 	 * to hot/cold instead of private/shared.
-- 
2.17.1

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Phil Auld]

Hi,

On Wed, Feb 14, 2024 at 12:53:55PM +0900 Byungchul Park wrote:
> While running qemu with a configuration where some CPUs don't have their
> local memory and with a kernel numa balancing on, the following oops has
> been observed. It's because of null pointers of ->zone_pgdat of zones of
> those nodes that are not initialized at booting time. So should avoid
> nodes not set N_MEMORY from getting promoted.
> 
> > 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>
> > Modules linked in:
> > CR2: 00000000000033f3
> > ---[ end trace 0000000000000000  ]---
> > 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
> > note: masim[895] exited with irqs disabled

I think you could trim the down a little bit.


> 
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Reported-by: hyeongtak.ji@sk.com
> ---
>  kernel/sched/fair.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d7a3c63a2171..6d215cc85f14 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1828,6 +1828,23 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
>  	int dst_nid = cpu_to_node(dst_cpu);
>  	int last_cpupid, this_cpupid;
>  
> +	/*
> +	 * A node of dst_nid might not have its local memory. Promoting
> +	 * a folio to the node is meaningless. What's even worse, oops
> +	 * can be observed by the null pointer of ->zone_pgdat in
> +	 * various points of the code during migration.
> +	 *

> +	 * For instance, oops has been observed at CPU2 while qemu'ing:
> +	 *
> +	 * {qemu} \
> +	 *    -numa node,nodeid=0,mem=1G,cpus=0-1 \
> +	 *    -numa node,nodeid=1,cpus=2-3 \
> +	 *    -numa node,nodeid=2,mem=8G \
> +	 *    ...

This part above should probably be in the commit message not in the code.
The first paragraph of comment is plenty.

Otherwise, I think the check probably makes sense.


Cheers,
Phil

> +	 */
> +	if (!node_state(dst_nid, N_MEMORY))
> +		return false;
> +
>  	/*
>  	 * The pages in slow memory node should be migrated according
>  	 * to hot/cold instead of private/shared.
> -- 
> 2.17.1
> 
> 

-- 

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Phil Auld]

On Wed, Feb 14, 2024 at 07:31:37AM -0500 Phil Auld wrote:
> Hi,
> 
> On Wed, Feb 14, 2024 at 12:53:55PM +0900 Byungchul Park wrote:
> > While running qemu with a configuration where some CPUs don't have their
> > local memory and with a kernel numa balancing on, the following oops has
> > been observed. It's because of null pointers of ->zone_pgdat of zones of
> > those nodes that are not initialized at booting time. So should avoid
> > nodes not set N_MEMORY from getting promoted.
> > 
> > > 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>
> > > Modules linked in:
> > > CR2: 00000000000033f3
> > > ---[ end trace 0000000000000000  ]---
> > > 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
> > > note: masim[895] exited with irqs disabled
> 
> I think you could trim the down a little bit.
> 
> 
> > 
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > Reported-by: hyeongtak.ji@sk.com
> > ---
> >  kernel/sched/fair.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d7a3c63a2171..6d215cc85f14 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1828,6 +1828,23 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
> >  	int dst_nid = cpu_to_node(dst_cpu);
> >  	int last_cpupid, this_cpupid;
> >  
> > +	/*
> > +	 * A node of dst_nid might not have its local memory. Promoting
> > +	 * a folio to the node is meaningless. What's even worse, oops
> > +	 * can be observed by the null pointer of ->zone_pgdat in
> > +	 * various points of the code during migration.
> > +	 *
> 
> > +	 * For instance, oops has been observed at CPU2 while qemu'ing:
> > +	 *
> > +	 * {qemu} \
> > +	 *    -numa node,nodeid=0,mem=1G,cpus=0-1 \
> > +	 *    -numa node,nodeid=1,cpus=2-3 \
> > +	 *    -numa node,nodeid=2,mem=8G \
> > +	 *    ...
> 
> This part above should probably be in the commit message not in the code.
> The first paragraph of comment is plenty.
> 
> Otherwise, I think the check probably makes sense.
>

Actually, after looking at the memory.c code I wonder if this check should
not be made farther up in the numa migrate machinery.


Cheers,
Phil

> 
> Cheers,
> Phil
> 
> > +	 */
> > +	if (!node_state(dst_nid, N_MEMORY))
> > +		return false;
> > +
> >  	/*
> >  	 * The pages in slow memory node should be migrated according
> >  	 * to hot/cold instead of private/shared.
> > -- 
> > 2.17.1
> > 
> > 
> 
> -- 
> 
> 

-- 

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Oscar Salvador]

On Wed, Feb 14, 2024 at 12:53:55PM +0900, Byungchul Park wrote:
> While running qemu with a configuration where some CPUs don't have their
> local memory and with a kernel numa balancing on, the following oops has
> been observed. It's because of null pointers of ->zone_pgdat of zones of
> those nodes that are not initialized at booting time. So should avoid
> nodes not set N_MEMORY from getting promoted.

Looking at free_area_init(), we call free_area_init_node() for each node
found on the system.
And free_area_init_node()->free_area_init_core() inits all zones
belonging to the system via zone_init_internals().
Now, I am not saying the check is wrong because we obviously do not want
migrate memory to a memoryless node, but I am confused as to where
we are crashing.


-- 
Oscar Salvador
SUSE Labs

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Wed, Feb 14, 2024 at 07:31:37AM -0500, Phil Auld wrote:
> Hi,
> 
> On Wed, Feb 14, 2024 at 12:53:55PM +0900 Byungchul Park wrote:
> > While running qemu with a configuration where some CPUs don't have their
> > local memory and with a kernel numa balancing on, the following oops has
> > been observed. It's because of null pointers of ->zone_pgdat of zones of
> > those nodes that are not initialized at booting time. So should avoid
> > nodes not set N_MEMORY from getting promoted.
> > 
> > > 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>
> > > Modules linked in:
> > > CR2: 00000000000033f3
> > > ---[ end trace 0000000000000000  ]---
> > > 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
> > > note: masim[895] exited with irqs disabled
> 
> I think you could trim the down a little bit.

Thank you for the feedback. I will.

> > 
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > Reported-by: hyeongtak.ji@sk.com
> > ---
> >  kernel/sched/fair.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d7a3c63a2171..6d215cc85f14 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1828,6 +1828,23 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
> >  	int dst_nid = cpu_to_node(dst_cpu);
> >  	int last_cpupid, this_cpupid;
> >  
> > +	/*
> > +	 * A node of dst_nid might not have its local memory. Promoting
> > +	 * a folio to the node is meaningless. What's even worse, oops
> > +	 * can be observed by the null pointer of ->zone_pgdat in
> > +	 * various points of the code during migration.
> > +	 *
> 
> > +	 * For instance, oops has been observed at CPU2 while qemu'ing:
> > +	 *
> > +	 * {qemu} \
> > +	 *    -numa node,nodeid=0,mem=1G,cpus=0-1 \
> > +	 *    -numa node,nodeid=1,cpus=2-3 \
> > +	 *    -numa node,nodeid=2,mem=8G \
> > +	 *    ...
> 
> This part above should probably be in the commit message not in the code.
> The first paragraph of comment is plenty.

I will.

Thanks. I will respin it.

	Byungchul

> Otherwise, I think the check probably makes sense.
> 
> 
> Cheers,
> Phil
> 
> > +	 */
> > +	if (!node_state(dst_nid, N_MEMORY))
> > +		return false;
> > +
> >  	/*
> >  	 * The pages in slow memory node should be migrated according
> >  	 * to hot/cold instead of private/shared.
> > -- 
> > 2.17.1
> > 
> > 
> 
> -- 

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Wed, Feb 14, 2024 at 10:13:57PM +0100, Oscar Salvador wrote:
> On Wed, Feb 14, 2024 at 12:53:55PM +0900, Byungchul Park wrote:
> > While running qemu with a configuration where some CPUs don't have their
> > local memory and with a kernel numa balancing on, the following oops has
> > been observed. It's because of null pointers of ->zone_pgdat of zones of
> > those nodes that are not initialized at booting time. So should avoid
> > nodes not set N_MEMORY from getting promoted.
> 
> Looking at free_area_init(), we call free_area_init_node() for each node
> found on the system.
> And free_area_init_node()->free_area_init_core() inits all zones
> belonging to the system via zone_init_internals().

For normal numa nodes, node_data[] is initialized at alloc_node_data(),
but it's not for memoryless node. However, the node *gets onlined* at
init_cpu_to_node().

Let's look at back free_area_init(). free_area_init_node() will be called
with node_data[] not set yet, because it's already *onlined*. So
->zone_pgdat cannot be initialized properly in the path you mentioned.

	Byungchul

> Now, I am not saying the check is wrong because we obviously do not want
> migrate memory to a memoryless node, but I am confused as to where
> we are crashing.
> 
> 
> -- 
> Oscar Salvador
> SUSE Labs

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Wed, Feb 14, 2024 at 03:03:18PM -0500, Phil Auld wrote:
> On Wed, Feb 14, 2024 at 07:31:37AM -0500 Phil Auld wrote:
> > Hi,
> > 
> > On Wed, Feb 14, 2024 at 12:53:55PM +0900 Byungchul Park wrote:
> > > While running qemu with a configuration where some CPUs don't have their
> > > local memory and with a kernel numa balancing on, the following oops has
> > > been observed. It's because of null pointers of ->zone_pgdat of zones of
> > > those nodes that are not initialized at booting time. So should avoid
> > > nodes not set N_MEMORY from getting promoted.
> > > 
> > > > 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>
> > > > Modules linked in:
> > > > CR2: 00000000000033f3
> > > > ---[ end trace 0000000000000000  ]---
> > > > 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
> > > > note: masim[895] exited with irqs disabled
> > 
> > I think you could trim the down a little bit.
> > 
> > 
> > > 
> > > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > > Reported-by: hyeongtak.ji@sk.com
> > > ---
> > >  kernel/sched/fair.c | 17 +++++++++++++++++
> > >  1 file changed, 17 insertions(+)
> > > 
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index d7a3c63a2171..6d215cc85f14 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -1828,6 +1828,23 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
> > >  	int dst_nid = cpu_to_node(dst_cpu);
> > >  	int last_cpupid, this_cpupid;
> > >  
> > > +	/*
> > > +	 * A node of dst_nid might not have its local memory. Promoting
> > > +	 * a folio to the node is meaningless. What's even worse, oops
> > > +	 * can be observed by the null pointer of ->zone_pgdat in
> > > +	 * various points of the code during migration.
> > > +	 *
> > 
> > > +	 * For instance, oops has been observed at CPU2 while qemu'ing:
> > > +	 *
> > > +	 * {qemu} \
> > > +	 *    -numa node,nodeid=0,mem=1G,cpus=0-1 \
> > > +	 *    -numa node,nodeid=1,cpus=2-3 \
> > > +	 *    -numa node,nodeid=2,mem=8G \
> > > +	 *    ...
> > 
> > This part above should probably be in the commit message not in the code.
> > The first paragraph of comment is plenty.
> > 
> > Otherwise, I think the check probably makes sense.
> >
> 
> Actually, after looking at the memory.c code I wonder if this check should
> not be made farther up in the numa migrate machinery.

First of all, we cannot avoid hinting fault. It's because no one knows
which node a task eventually runs on until a hinting fault occurs. So
should let it go get hinting fault *and then* we can make the decision
if we can migrate the folio or not. Assuming that, IMHO,
should_numa_migrate_memory() is a good place to make it.

Thoughts? Am I missing something?

	Byungchul

> Cheers,
> Phil
> 
> > 
> > Cheers,
> > Phil
> > 
> > > +	 */
> > > +	if (!node_state(dst_nid, N_MEMORY))
> > > +		return false;
> > > +
> > >  	/*
> > >  	 * The pages in slow memory node should be migrated according
> > >  	 * to hot/cold instead of private/shared.
> > > -- 
> > > 2.17.1
> > > 
> > > 
> > 
> > -- 
> > 
> > 
> 
> -- 

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Oscar Salvador]

On Fri, Feb 16, 2024 at 04:07:54PM +0900, Byungchul Park wrote:
> For normal numa nodes, node_data[] is initialized at alloc_node_data(),
> but it's not for memoryless node. However, the node *gets onlined* at
> init_cpu_to_node().
> 
> Let's look at back free_area_init(). free_area_init_node() will be called
> with node_data[] not set yet, because it's already *onlined*. So
> ->zone_pgdat cannot be initialized properly in the path you mentioned.

I am might be missing something., so bear with me.

free_area_init() gets called before init_cpu_to_node() does.
free_area_init_node() gets called on every possible node.

free_area_init_node then() does

 pg_data_t *pgdat = NODE_DATA(nid);,

and then we call free_area_init_core().

free_area_init_core() does

 free_area_init_core() does
  zone_init_internals()

which ends up doing zone->zone_pgdat = NODE_DATA(nid);

If node_data[] was not set at all, we would already blow up when doing
the first

  for_each_node()
    pgdat = NODE_DATA(nid);
    free_area_init_node(nid);

back in free_area_init().


-- 
Oscar Salvador
SUSE Labs

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Fri, Feb 16, 2024 at 08:52:30AM +0100, Oscar Salvador wrote:
> On Fri, Feb 16, 2024 at 04:07:54PM +0900, Byungchul Park wrote:
> > For normal numa nodes, node_data[] is initialized at alloc_node_data(),
> > but it's not for memoryless node. However, the node *gets onlined* at
> > init_cpu_to_node().
> > 
> > Let's look at back free_area_init(). free_area_init_node() will be called
> > with node_data[] not set yet, because it's already *onlined*. So
> > ->zone_pgdat cannot be initialized properly in the path you mentioned.
> 
> I am might be missing something., so bear with me.
> 
> free_area_init() gets called before init_cpu_to_node() does.
> free_area_init_node() gets called on every possible node.
> 
> free_area_init_node then() does
> 
>  pg_data_t *pgdat = NODE_DATA(nid);,
> 
> and then we call free_area_init_core().
> 
> free_area_init_core() does
> 
>  free_area_init_core() does
>   zone_init_internals()
> 
> which ends up doing zone->zone_pgdat = NODE_DATA(nid);
> 
> If node_data[] was not set at all, we would already blow up when doing
> the first
> 
>   for_each_node()
>     pgdat = NODE_DATA(nid);
>     free_area_init_node(nid);
> 
> back in free_area_init().

It seems that I got it wrong about the reason. Let me check it again and
share the reason.

Just in case, this patch is still definitely necessary tho.

	Byungchul

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Fri, Feb 16, 2024 at 06:11:40PM +0900, Byungchul Park wrote:
> On Fri, Feb 16, 2024 at 08:52:30AM +0100, Oscar Salvador wrote:
> > On Fri, Feb 16, 2024 at 04:07:54PM +0900, Byungchul Park wrote:
> > > For normal numa nodes, node_data[] is initialized at alloc_node_data(),
> > > but it's not for memoryless node. However, the node *gets onlined* at
> > > init_cpu_to_node().
> > > 
> > > Let's look at back free_area_init(). free_area_init_node() will be called
> > > with node_data[] not set yet, because it's already *onlined*. So
> > > ->zone_pgdat cannot be initialized properly in the path you mentioned.
> > 
> > I am might be missing something., so bear with me.
> > 
> > free_area_init() gets called before init_cpu_to_node() does.
> > free_area_init_node() gets called on every possible node.
> > 
> > free_area_init_node then() does
> > 
> >  pg_data_t *pgdat = NODE_DATA(nid);,
> > 
> > and then we call free_area_init_core().
> > 
> > free_area_init_core() does
> > 
> >  free_area_init_core() does
> >   zone_init_internals()
> > 
> > which ends up doing zone->zone_pgdat = NODE_DATA(nid);
> > 
> > If node_data[] was not set at all, we would already blow up when doing
> > the first
> > 
> >   for_each_node()
> >     pgdat = NODE_DATA(nid);
> >     free_area_init_node(nid);
> > 
> > back in free_area_init().
> 
> It seems that I got it wrong about the reason. Let me check it again and
> share the reason.
> 
> Just in case, this patch is still definitely necessary tho.

Sorry for the confusing expression. Please don't misunderstand it. The
oops has been always observed in the configuration that I descriped. I
meant:

   Just in case, I need to say the fix is still necessary.

	Byungchul

Re: [PATCH] sched/numa, mm: do not promote folios to nodes not set N_MEMORY

[Byungchul Park]

On Fri, Feb 16, 2024 at 06:23:05PM +0900, Byungchul Park wrote:
> On Fri, Feb 16, 2024 at 06:11:40PM +0900, Byungchul Park wrote:
> > On Fri, Feb 16, 2024 at 08:52:30AM +0100, Oscar Salvador wrote:
> > > On Fri, Feb 16, 2024 at 04:07:54PM +0900, Byungchul Park wrote:
> > > > For normal numa nodes, node_data[] is initialized at alloc_node_data(),
> > > > but it's not for memoryless node. However, the node *gets onlined* at
> > > > init_cpu_to_node().
> > > > 
> > > > Let's look at back free_area_init(). free_area_init_node() will be called
> > > > with node_data[] not set yet, because it's already *onlined*. So
> > > > ->zone_pgdat cannot be initialized properly in the path you mentioned.
> > > 
> > > I am might be missing something., so bear with me.
> > > 
> > > free_area_init() gets called before init_cpu_to_node() does.
> > > free_area_init_node() gets called on every possible node.
> > > 
> > > free_area_init_node then() does
> > > 
> > >  pg_data_t *pgdat = NODE_DATA(nid);,
> > > 
> > > and then we call free_area_init_core().
> > > 
> > > free_area_init_core() does
> > > 
> > >  free_area_init_core() does
> > >   zone_init_internals()
> > > 
> > > which ends up doing zone->zone_pgdat = NODE_DATA(nid);
> > > 
> > > If node_data[] was not set at all, we would already blow up when doing
> > > the first
> > > 
> > >   for_each_node()
> > >     pgdat = NODE_DATA(nid);
> > >     free_area_init_node(nid);
> > > 
> > > back in free_area_init().
> > 
> > It seems that I got it wrong about the reason. Let me check it again and
> > share the reason.

I analyzed it wrong. Even though the issue was gone with the patch but
it's not the fix. Sorry for making you confused. I submitted the fix with
another patch:

   https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/

	Byungchul