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mm/damon/ops-common: ignore migration request to invalid nodes

PATCH Applied SeongJae Park 3 participants 5 messages Jul 20, 2025 – Jul 22, 2025

Subsystems (3)
Stable branch Memory management DAMON
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SeongJae Park

author maintainer
#0 lore raw

PATCH 1/1 mm/damon/ops-common: ignore migration request to invalid nodes

damon_migrate_pages() try migration even if the target node is invalid. If users mistakenly make such invalid requests via DAMOS_MIGRATE_{HOT,COLD} action, below kernel BUG can happen.

    [ 7831.883495] BUG: unable to handle page fault for address: 0000000000001f48
    [ 7831.884160] #PF: supervisor read access in kernel mode
    [ 7831.884681] #PF: error_code(0x0000) - not-present page
    [ 7831.885203] PGD 0 P4D 0
    [ 7831.885468] Oops: Oops: 0000 [#1] SMP PTI
    [ 7831.885852] CPU: 31 UID: 0 PID: 94202 Comm: kdamond.0 Not tainted 6.16.0-rc5-mm-new-damon+ #93 PREEMPT(voluntary)
    [ 7831.886913] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.el9 04/01/2014
    [ 7831.887777] RIP: 0010:__alloc_frozen_pages_noprof (include/linux/mmzone.h:1724 include/linux/mmzone.h:1750 mm/page_alloc.c:4936 mm/page_alloc.c:5137)
    [...]
    [ 7831.895953] Call Trace:
    [ 7831.896195]  <TASK>
    [ 7831.896397] __folio_alloc_noprof (mm/page_alloc.c:5183 mm/page_alloc.c:5192)
    [ 7831.896787] migrate_pages_batch (mm/migrate.c:1189 mm/migrate.c:1851)
    [ 7831.897228] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.897735] migrate_pages (mm/migrate.c:2078)
    [ 7831.898141] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.898664] damon_migrate_folio_list (mm/damon/ops-common.c:321 mm/damon/ops-common.c:354)
    [ 7831.899140] damon_migrate_pages (mm/damon/ops-common.c:405)
    [...]

Add a target node validity check in damon_migrate_pages(). The validity check is stolen from that of do_pages_move(), which is being used for move_pages() system call.

Fixes b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") # 6.11.x
Cc [email protected]
Cc Honggyu Kim <[email protected]>
Signed-off-by SeongJae Park <[email protected]>
---
 mm/damon/ops-common.c | 4 ++++
 1 file changed, 4 insertions(+)
mm/damon/ops-common.c +4 -0
index 6a9797d1d7ff..99321ff5cb92 100644
@@ -383,6 +383,10 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
 	if (list_empty(folio_list))
 		return nr_migrated;
 
+	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
+			!node_state(target_nid, N_MEMORY))
+		return nr_migrated;
+
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	nid = folio_nid(lru_to_folio(folio_list));

base-commit: e2c90d41402c324ea81fa3d9c2c1d0f61906c161

Signature · 1 line
2.39.5
Reviewed-by on v1 1/1
#1 lore raw
Quoted 28 lines · On Sun, 20 Jul 2025 11:58:22 -0700 SeongJae Park <[email protected]> wrote:

damon_migrate_pages() try migration even if the target node is invalid. If users mistakenly make such invalid requests via DAMOS_MIGRATE_{HOT,COLD} action, below kernel BUG can happen.

    [ 7831.883495] BUG: unable to handle page fault for address: 0000000000001f48
    [ 7831.884160] #PF: supervisor read access in kernel mode
    [ 7831.884681] #PF: error_code(0x0000) - not-present page
    [ 7831.885203] PGD 0 P4D 0
    [ 7831.885468] Oops: Oops: 0000 [#1] SMP PTI
    [ 7831.885852] CPU: 31 UID: 0 PID: 94202 Comm: kdamond.0 Not tainted 6.16.0-rc5-mm-new-damon+ #93 PREEMPT(voluntary)
    [ 7831.886913] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.el9 04/01/2014
    [ 7831.887777] RIP: 0010:__alloc_frozen_pages_noprof (include/linux/mmzone.h:1724 include/linux/mmzone.h:1750 mm/page_alloc.c:4936 mm/page_alloc.c:5137)
    [...]
    [ 7831.895953] Call Trace:
    [ 7831.896195]  <TASK>
    [ 7831.896397] __folio_alloc_noprof (mm/page_alloc.c:5183 mm/page_alloc.c:5192)
    [ 7831.896787] migrate_pages_batch (mm/migrate.c:1189 mm/migrate.c:1851)
    [ 7831.897228] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.897735] migrate_pages (mm/migrate.c:2078)
    [ 7831.898141] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.898664] damon_migrate_folio_list (mm/damon/ops-common.c:321 mm/damon/ops-common.c:354)
    [ 7831.899140] damon_migrate_pages (mm/damon/ops-common.c:405)
    [...]

Add a target node validity check in damon_migrate_pages(). The validity check is stolen from that of do_pages_move(), which is being used for move_pages() system call.

Quoted 5 lines
Fixes b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") # 6.11.x
Cc [email protected]
Cc Honggyu Kim <[email protected]>
Signed-off-by SeongJae Park <[email protected]>

---

LGTM, thank you SJ!

On a side note... This seems like it would be a common check. However, doing a (quick) search seems to return no function that checks whether a node is valid. Perhaps it would make sense to look deeper and see how many other functions make this check, and export this as a function? I can try spinning something if it makes sense to you : -)

Reviewed-by Joshua Hahn <[email protected]>

Sent using hkml (https://github.com/sjp38/hackermail)

author maintainer
#2 lore raw
Quoted 5 lines · On Mon, 21 Jul 2025 08:28:26 -0700 Joshua Hahn <[email protected]> wrote:
Quoted 3 lines · On Sun, 20 Jul 2025 11:58:22 -0700 SeongJae Park <[email protected]> wrote:

damon_migrate_pages() try migration even if the target node is invalid. If users mistakenly make such invalid requests via DAMOS_MIGRATE_{HOT,COLD} action, below kernel BUG can happen.

[...]

Quoted 10 lines
Quoted 9 lines

Add a target node validity check in damon_migrate_pages(). The validity check is stolen from that of do_pages_move(), which is being used for move_pages() system call.

Fixes b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") # 6.11.x
Cc [email protected]
Cc Honggyu Kim <[email protected]>
Signed-off-by SeongJae Park <[email protected]>

---

Quoted 7 lines

LGTM, thank you SJ!

On a side note... This seems like it would be a common check. However, doing a (quick) search seems to return no function that checks whether a node is valid. Perhaps it would make sense to look deeper and see how many other functions make this check, and export this as a function? I can try spinning something if it makes sense to you : -)

My humble impression was that this check is short enough to be ok to be open-coded, but please don't be blocked on my opinion :)

Quoted 2 lines
Reviewed-by Joshua Hahn <[email protected]>

Thank you!

Quoted 2 lines

Sent using hkml (https://github.com/sjp38/hackermail)

Thanks,
SJ

maintainer
#3 lore raw
In reply to SeongJae Park
Quoted 37 lines · On Sun, 20 Jul 2025 11:58:22 -0700 SeongJae Park <[email protected]> wrote:

damon_migrate_pages() try migration even if the target node is invalid. If users mistakenly make such invalid requests via DAMOS_MIGRATE_{HOT,COLD} action, below kernel BUG can happen.

    [ 7831.883495] BUG: unable to handle page fault for address: 0000000000001f48
    [ 7831.884160] #PF: supervisor read access in kernel mode
    [ 7831.884681] #PF: error_code(0x0000) - not-present page
    [ 7831.885203] PGD 0 P4D 0
    [ 7831.885468] Oops: Oops: 0000 [#1] SMP PTI
    [ 7831.885852] CPU: 31 UID: 0 PID: 94202 Comm: kdamond.0 Not tainted 6.16.0-rc5-mm-new-damon+ #93 PREEMPT(voluntary)
    [ 7831.886913] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.el9 04/01/2014
    [ 7831.887777] RIP: 0010:__alloc_frozen_pages_noprof (include/linux/mmzone.h:1724 include/linux/mmzone.h:1750 mm/page_alloc.c:4936 mm/page_alloc.c:5137)
    [...]
    [ 7831.895953] Call Trace:
    [ 7831.896195]  <TASK>
    [ 7831.896397] __folio_alloc_noprof (mm/page_alloc.c:5183 mm/page_alloc.c:5192)
    [ 7831.896787] migrate_pages_batch (mm/migrate.c:1189 mm/migrate.c:1851)
    [ 7831.897228] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.897735] migrate_pages (mm/migrate.c:2078)
    [ 7831.898141] ? __pfx_alloc_migration_target (mm/migrate.c:2137)
    [ 7831.898664] damon_migrate_folio_list (mm/damon/ops-common.c:321 mm/damon/ops-common.c:354)
    [ 7831.899140] damon_migrate_pages (mm/damon/ops-common.c:405)
    [...]

Add a target node validity check in damon_migrate_pages(). The validity check is stolen from that of do_pages_move(), which is being used for move_pages() system call.

Fixes b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") # 6.11.x
Cc [email protected]

...

mm/damon/ops-common.c unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid) · line 392

Quoted 10 lines
mm/damon/ops-common.c +4 -0
@@ -383,6 +383,10 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
 	if (list_empty(folio_list))
 		return nr_migrated;
 
+	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
+			!node_state(target_nid, N_MEMORY))
+		return nr_migrated;
+
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	nid = folio_nid(lru_to_folio(folio_list));

OK. damon_migrate_pages() exists only in mm.git thanks to 13dde31db71f ("mm/damon: move migration helpers from paddr to ops-common"). I assume that you'll send the -stable people a patch which adds this check into damon_pa_migrate_pages() when called upon to do so.

author maintainer
#4 lore raw
Quoted 2 lines · On Mon, 21 Jul 2025 19:56:58 -0700 Andrew Morton <[email protected]>…

On Sun, 20 Jul 2025 11:58:22 -0700 SeongJae Park <[email protected]> wrote:

[...]

Quoted 21 lines
Quoted 21 lines

Add a target node validity check in damon_migrate_pages(). The validity check is stolen from that of do_pages_move(), which is being used for move_pages() system call.

Fixes b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") # 6.11.x
Cc [email protected]

...

mm/damon/ops-common.c +4 -0
@@ -383,6 +383,10 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
 	if (list_empty(folio_list))
 		return nr_migrated;
 
+	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
+			!node_state(target_nid, N_MEMORY))
+		return nr_migrated;
+
 	noreclaim_flag = memalloc_noreclaim_save();
Quoted 7 lines

mm/damon/ops-common.c unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid) · line 392

Quoted 2 lines
mm/damon/ops-common.c +0 -0
 	nid = folio_nid(lru_to_folio(folio_list));

OK. damon_migrate_pages() exists only in mm.git thanks to 13dde31db71f ("mm/damon: move migration helpers from paddr to ops-common"). I assume that you'll send the -stable people a patch which adds this check into damon_pa_migrate_pages() when called upon to do so.

That's very correct, Andrew. I am planning to do so as soon as this is merged into the mainline :)

Thanks,
SJ