* [PATCH 5.15] mm: replace free hugepage folios after migration
@ 2026-11-05 7:02 Mark Bundschuh
2026-11-06 7:46 ` David Hildenbrand (Arm)
2026-11-06 22:04 ` [PATCH v2 5.15 0/2] " Mark Bundschuh
0 siblings, 2 replies; 5+ messages in thread
From: Mark Bundschuh @ 2026-11-05 7:02 UTC (permalink / raw)
To: stable
Cc: linux-mm, david, yangge, Baolin Wang, Barry Song,
David Hildenbrand, SeongJae Park, Andrew Morton, Mark Bundschuh
From: yangge <yangge1116@126.com>
[ Upstream commit 04f13d241b8b146b23038bffd907cb8278391d07 ]
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have
configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb
pages. The allocation of contiguous memory via cma_alloc() can fail
probabilistically.
When there are free hugetlb folios in the hugetlb pool, during the
migration of in-use hugetlb folios, new folios are allocated from the free
hugetlb pool. After the migration is completed, the old folios are
released back to the free hugetlb pool instead of being returned to the
buddy system. This can cause test_pages_isolated() check to fail,
ultimately leading to the failure of cma_alloc().
Call trace:
cma_alloc()
__alloc_contig_migrate_range() // migrate in-use hugepage
test_pages_isolated()
__test_page_isolated_in_pageblock()
PageBuddy(page) // check if the page is in buddy
To address this issue, we introduce a function named
replace_free_hugepage_folios(). This function will replace the hugepage
in the free hugepage pool with a new one and release the old one to the
buddy system. After the migration of in-use hugetlb pages is completed,
we will invoke replace_free_hugepage_folios() to ensure that these
hugepages are properly released to the buddy system. Following this step,
when test_pages_isolated() is executed for inspection, it will
successfully pass.
Additionally, when alloc_contig_range() is used to migrate multiple in-use
hugetlb pages, it can result in some in-use hugetlb pages being released
back to the free hugetlb pool and subsequently being reallocated and used
again. For example:
[huge 0] [huge 1]
To migrate huge 0, we obtain huge x from the pool. After the migration is
completed, we return the now-freed huge 0 back to the pool. When it's
time to migrate huge 1, we can simply reuse the now-freed huge 0 from the
pool. As a result, when replace_free_hugepage_folios() is executed, it
cannot release huge 0 back to the buddy system. To address this issue, we
should prevent the reuse of isolated free hugepages during the migration
process.
Link: https://lkml.kernel.org/r/1734503588-16254-1-git-send-email-yangge1116@126.com
Link: https://lkml.kernel.org/r/1736582300-11364-1-git-send-email-yangge1116@126.com
Signed-off-by: yangge <yangge1116@126.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ 5.15: Take only the dequeue_huge_page_node_exact() hunk, so memory
offline stops migrating huge pages back into the isolated range. ]
Signed-off-by: Mark Bundschuh <mkbund@amazon.com>
---
Without this, offlining a memory block holding mapped huge pages keeps
migrating them back into the block until the offline is interrupted.
Reproduced on arm64 on 5.10 and 6.12 (stock AL2023 6.12.113): the offline
was still migrating after 60 s. With this patch on 5.10 it completes in
0.15 s with the data intact. Also sent for 5.10, 5.15, 6.1, 6.6 and 6.12.
mm/hugetlb.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 947610e37a33..6df31569ce36 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -43,6 +43,7 @@
#include <linux/page_owner.h>
#include "internal.h"
#include "hugetlb_vmemmap.h"
+#include <linux/page-isolation.h>
int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
@@ -1095,6 +1096,9 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
if (PageHWPoison(page))
continue;
+ if (is_migrate_isolate_page(page))
+ continue;
+
list_move(&page->lru, &h->hugepage_activelist);
set_page_refcounted(page);
ClearHPageFreed(page);
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 5.15] mm: replace free hugepage folios after migration
2026-11-05 7:02 [PATCH 5.15] mm: replace free hugepage folios after migration Mark Bundschuh
@ 2026-11-06 7:46 ` David Hildenbrand (Arm)
2026-11-06 22:04 ` [PATCH v2 5.15 0/2] " Mark Bundschuh
1 sibling, 0 replies; 5+ messages in thread
From: David Hildenbrand (Arm) @ 2026-11-06 7:46 UTC (permalink / raw)
To: Mark Bundschuh, stable
Cc: linux-mm, yangge, Baolin Wang, Barry Song, SeongJae Park,
Andrew Morton
On 11/5/26 08:02, Mark Bundschuh wrote:
> From: yangge <yangge1116@126.com>
>
> [ Upstream commit 04f13d241b8b146b23038bffd907cb8278391d07 ]
>
> My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have
> configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb
> pages. The allocation of contiguous memory via cma_alloc() can fail
> probabilistically.
>
> When there are free hugetlb folios in the hugetlb pool, during the
> migration of in-use hugetlb folios, new folios are allocated from the free
> hugetlb pool. After the migration is completed, the old folios are
> released back to the free hugetlb pool instead of being returned to the
> buddy system. This can cause test_pages_isolated() check to fail,
> ultimately leading to the failure of cma_alloc().
>
> Call trace:
>
> cma_alloc()
> __alloc_contig_migrate_range() // migrate in-use hugepage
> test_pages_isolated()
> __test_page_isolated_in_pageblock()
> PageBuddy(page) // check if the page is in buddy
>
> To address this issue, we introduce a function named
> replace_free_hugepage_folios(). This function will replace the hugepage
> in the free hugepage pool with a new one and release the old one to the
> buddy system. After the migration of in-use hugetlb pages is completed,
> we will invoke replace_free_hugepage_folios() to ensure that these
> hugepages are properly released to the buddy system. Following this step,
> when test_pages_isolated() is executed for inspection, it will
> successfully pass.
>
> Additionally, when alloc_contig_range() is used to migrate multiple in-use
> hugetlb pages, it can result in some in-use hugetlb pages being released
> back to the free hugetlb pool and subsequently being reallocated and used
> again. For example:
>
> [huge 0] [huge 1]
>
> To migrate huge 0, we obtain huge x from the pool. After the migration is
> completed, we return the now-freed huge 0 back to the pool. When it's
> time to migrate huge 1, we can simply reuse the now-freed huge 0 from the
> pool. As a result, when replace_free_hugepage_folios() is executed, it
> cannot release huge 0 back to the buddy system. To address this issue, we
> should prevent the reuse of isolated free hugepages during the migration
> process.
>
> Link: https://lkml.kernel.org/r/1734503588-16254-1-git-send-email-yangge1116@126.com
> Link: https://lkml.kernel.org/r/1736582300-11364-1-git-send-email-yangge1116@126.com
> Signed-off-by: yangge <yangge1116@126.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Barry Song <21cnbao@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: SeongJae Park <sj@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> [ 5.15: Take only the dequeue_huge_page_node_exact() hunk, so memory
> offline stops migrating huge pages back into the isolated range. ]
> Signed-off-by: Mark Bundschuh <mkbund@amazon.com>
> ---
> Without this, offlining a memory block holding mapped huge pages keeps
> migrating them back into the block until the offline is interrupted.
> Reproduced on arm64 on 5.10 and 6.12 (stock AL2023 6.12.113): the offline
> was still migrating after 60 s. With this patch on 5.10 it completes in
> 0.15 s with the data intact. Also sent for 5.10, 5.15, 6.1, 6.6 and 6.12.
The simplified backport was really only the right thing to do for 5.10, per my
other mail.
--
Cheers,
David
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2 5.15 0/2] mm: replace free hugepage folios after migration
2026-11-05 7:02 [PATCH 5.15] mm: replace free hugepage folios after migration Mark Bundschuh
2026-11-06 7:46 ` David Hildenbrand (Arm)
@ 2026-11-06 22:04 ` Mark Bundschuh
2026-11-06 22:04 ` [PATCH v2 5.15 1/2] " Mark Bundschuh
2026-11-06 22:04 ` [PATCH v2 5.15 2/2] mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios Mark Bundschuh
1 sibling, 2 replies; 5+ messages in thread
From: Mark Bundschuh @ 2026-11-06 22:04 UTC (permalink / raw)
To: stable; +Cc: sashal, linux-mm, david, Mark Bundschuh
Full backport of 04f13d241b8b ("mm: replace free hugepage folios after
migration") with its fix 113ed54ad276.
Tested in a VM on 5.15.224: memory offline of a block with mapped huge
pages no longer livelocks, and cma_alloc() over mapped huge pages now
succeeds (it failed on 5.15.224 and with v1).
v1: https://lore.kernel.org/all/20261105070206.3094675-1-mkbund@amazon.com/
Ge Yang (1):
mm/hugetlb: fix kernel NULL pointer dereference when replacing free
hugetlb folios
yangge (1):
mm: replace free hugepage folios after migration
include/linux/hugetlb.h | 7 ++++++
mm/hugetlb.c | 49 +++++++++++++++++++++++++++++++++++++++++
mm/page_alloc.c | 12 +++++++++-
3 files changed, 67 insertions(+), 1 deletion(-)
--
2.50.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2 5.15 1/2] mm: replace free hugepage folios after migration
2026-11-06 22:04 ` [PATCH v2 5.15 0/2] " Mark Bundschuh
@ 2026-11-06 22:04 ` Mark Bundschuh
2026-11-06 22:04 ` [PATCH v2 5.15 2/2] mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios Mark Bundschuh
1 sibling, 0 replies; 5+ messages in thread
From: Mark Bundschuh @ 2026-11-06 22:04 UTC (permalink / raw)
To: stable
Cc: sashal, linux-mm, david, yangge, Baolin Wang, Barry Song,
David Hildenbrand, SeongJae Park, Andrew Morton, Mark Bundschuh
From: yangge <yangge1116@126.com>
[ Upstream commit 04f13d241b8b146b23038bffd907cb8278391d07 ]
My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have
configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb
pages. The allocation of contiguous memory via cma_alloc() can fail
probabilistically.
When there are free hugetlb folios in the hugetlb pool, during the
migration of in-use hugetlb folios, new folios are allocated from the free
hugetlb pool. After the migration is completed, the old folios are
released back to the free hugetlb pool instead of being returned to the
buddy system. This can cause test_pages_isolated() check to fail,
ultimately leading to the failure of cma_alloc().
Call trace:
cma_alloc()
__alloc_contig_migrate_range() // migrate in-use hugepage
test_pages_isolated()
__test_page_isolated_in_pageblock()
PageBuddy(page) // check if the page is in buddy
To address this issue, we introduce a function named
replace_free_hugepage_folios(). This function will replace the hugepage
in the free hugepage pool with a new one and release the old one to the
buddy system. After the migration of in-use hugetlb pages is completed,
we will invoke replace_free_hugepage_folios() to ensure that these
hugepages are properly released to the buddy system. Following this step,
when test_pages_isolated() is executed for inspection, it will
successfully pass.
Additionally, when alloc_contig_range() is used to migrate multiple in-use
hugetlb pages, it can result in some in-use hugetlb pages being released
back to the free hugetlb pool and subsequently being reallocated and used
again. For example:
[huge 0] [huge 1]
To migrate huge 0, we obtain huge x from the pool. After the migration is
completed, we return the now-freed huge 0 back to the pool. When it's
time to migrate huge 1, we can simply reuse the now-freed huge 0 from the
pool. As a result, when replace_free_hugepage_folios() is executed, it
cannot release huge 0 back to the buddy system. To address this issue, we
should prevent the reuse of isolated free hugepages during the migration
process.
Link: https://lkml.kernel.org/r/1734503588-16254-1-git-send-email-yangge1116@126.com
Link: https://lkml.kernel.org/r/1736582300-11364-1-git-send-email-yangge1116@126.com
Signed-off-by: yangge <yangge1116@126.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ 5.15: Use pages instead of folios. ]
Signed-off-by: Mark Bundschuh <mkbund@amazon.com>
---
include/linux/hugetlb.h | 7 +++++++
mm/hugetlb.c | 41 +++++++++++++++++++++++++++++++++++++++++
mm/page_alloc.c | 12 +++++++++++-
3 files changed, 59 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 254fcd6f9604..e4b6aa016d30 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -641,6 +641,7 @@ struct huge_bootmem_page {
};
int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn);
struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr, int avoid_reserve);
struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
@@ -933,6 +934,12 @@ static inline int isolate_or_dissolve_huge_page(struct page *page,
return -ENOMEM;
}
+static inline int replace_free_hugepage_folios(unsigned long start_pfn,
+ unsigned long end_pfn)
+{
+ return 0;
+}
+
static inline struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr,
int avoid_reserve)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 947610e37a33..4fb98320f9df 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -43,6 +43,7 @@
#include <linux/page_owner.h>
#include "internal.h"
#include "hugetlb_vmemmap.h"
+#include <linux/page-isolation.h>
int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
@@ -1095,6 +1096,9 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
if (PageHWPoison(page))
continue;
+ if (is_migrate_isolate_page(page))
+ continue;
+
list_move(&page->lru, &h->hugepage_activelist);
set_page_refcounted(page);
ClearHPageFreed(page);
@@ -2735,6 +2739,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
return ret;
}
+/*
+ * replace_free_hugepage_folios - Replace free hugepage folios in a given pfn
+ * range with new folios.
+ * @start_pfn: start pfn of the given pfn range
+ * @end_pfn: end pfn of the given pfn range
+ * Returns 0 on success, otherwise negated error.
+ */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
+{
+ struct hstate *h;
+ struct page *page;
+ int ret = 0;
+
+ LIST_HEAD(isolate_list);
+
+ while (start_pfn < end_pfn) {
+ page = compound_head(pfn_to_page(start_pfn));
+ if (PageHuge(page)) {
+ h = page_hstate(page);
+ } else {
+ start_pfn++;
+ continue;
+ }
+
+ if (!page_count(page)) {
+ ret = alloc_and_dissolve_huge_page(h, page, &isolate_list);
+ if (ret)
+ break;
+
+ putback_movable_pages(&isolate_list);
+ }
+ start_pfn++;
+ }
+
+ return ret;
+}
+
struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr, int avoid_reserve)
{
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cfbfd6309c25..b813570d2b39 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9250,7 +9250,17 @@ int alloc_contig_range(unsigned long start, unsigned long end,
ret = __alloc_contig_migrate_range(&cc, start, end);
if (ret && ret != -EBUSY)
goto done;
- ret = 0;
+
+ /*
+ * When in-use hugetlb pages are migrated, they may simply be released
+ * back into the free hugepage pool instead of being returned to the
+ * buddy system. After the migration of in-use huge pages is completed,
+ * we will invoke replace_free_hugepage_folios() to ensure that these
+ * hugepages are properly released to the buddy system.
+ */
+ ret = replace_free_hugepage_folios(start, end);
+ if (ret)
+ goto done;
/*
* Pages from [start, end) are within a MAX_ORDER_NR_PAGES
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2 5.15 2/2] mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios
2026-11-06 22:04 ` [PATCH v2 5.15 0/2] " Mark Bundschuh
2026-11-06 22:04 ` [PATCH v2 5.15 1/2] " Mark Bundschuh
@ 2026-11-06 22:04 ` Mark Bundschuh
1 sibling, 0 replies; 5+ messages in thread
From: Mark Bundschuh @ 2026-11-06 22:04 UTC (permalink / raw)
To: stable
Cc: sashal, linux-mm, david, Ge Yang, Muchun Song, Oscar Salvador,
Baolin Wang, Barry Song, David Hildenbrand, Andrew Morton,
Mark Bundschuh
From: Ge Yang <yangge1116@126.com>
[ Upstream commit 113ed54ad276c352ee5ce109bdcf0df118a43bda ]
A kernel crash was observed when replacing free hugetlb folios:
BUG: kernel NULL pointer dereference, address: 0000000000000028
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 28 UID: 0 PID: 29639 Comm: test_cma.sh Tainted 6.15.0-rc6-zp #41 PREEMPT(voluntary)
RIP: 0010:alloc_and_dissolve_hugetlb_folio+0x1d/0x1f0
RSP: 0018:ffffc9000b30fa90 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000342cca RCX: ffffea0043000000
RDX: ffffc9000b30fb08 RSI: ffffea0043000000 RDI: 0000000000000000
RBP: ffffc9000b30fb20 R08: 0000000000001000 R09: 0000000000000000
R10: ffff88886f92eb00 R11: 0000000000000000 R12: ffffea0043000000
R13: 0000000000000000 R14: 00000000010c0200 R15: 0000000000000004
FS: 00007fcda5f14740(0000) GS:ffff8888ec1d8000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 0000000391402000 CR4: 0000000000350ef0
Call Trace:
<TASK>
replace_free_hugepage_folios+0xb6/0x100
alloc_contig_range_noprof+0x18a/0x590
? srso_return_thunk+0x5/0x5f
? down_read+0x12/0xa0
? srso_return_thunk+0x5/0x5f
cma_range_alloc.constprop.0+0x131/0x290
__cma_alloc+0xcf/0x2c0
cma_alloc_write+0x43/0xb0
simple_attr_write_xsigned.constprop.0.isra.0+0xb2/0x110
debugfs_attr_write+0x46/0x70
full_proxy_write+0x62/0xa0
vfs_write+0xf8/0x420
? srso_return_thunk+0x5/0x5f
? filp_flush+0x86/0xa0
? srso_return_thunk+0x5/0x5f
? filp_close+0x1f/0x30
? srso_return_thunk+0x5/0x5f
? do_dup2+0xaf/0x160
? srso_return_thunk+0x5/0x5f
ksys_write+0x65/0xe0
do_syscall_64+0x64/0x170
entry_SYSCALL_64_after_hwframe+0x76/0x7e
There is a potential race between __update_and_free_hugetlb_folio() and
replace_free_hugepage_folios():
CPU1 CPU2
__update_and_free_hugetlb_folio replace_free_hugepage_folios
folio_test_hugetlb(folio)
-- It's still hugetlb folio.
__folio_clear_hugetlb(folio)
hugetlb_free_folio(folio)
h = folio_hstate(folio)
-- Here, h is NULL pointer
When the above race condition occurs, folio_hstate(folio) returns NULL,
and subsequent access to this NULL pointer will cause the system to crash.
To resolve this issue, execute folio_hstate(folio) under the protection
of the hugetlb_lock lock, ensuring that folio_hstate(folio) does not
return NULL.
Link: https://lkml.kernel.org/r/1747884137-26685-1-git-send-email-yangge1116@126.com
Fixes: 04f13d241b8b ("mm: replace free hugepage folios after migration")
Signed-off-by: Ge Yang <yangge1116@126.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ 5.15: Use pages instead of folios. ]
Signed-off-by: Mark Bundschuh <mkbund@amazon.com>
---
mm/hugetlb.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4fb98320f9df..3d7e8826e452 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2756,12 +2756,20 @@ int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
while (start_pfn < end_pfn) {
page = compound_head(pfn_to_page(start_pfn));
+
+ /*
+ * The page might have been dissolved from under our feet, so make sure
+ * to carefully check the state under the lock.
+ */
+ spin_lock_irq(&hugetlb_lock);
if (PageHuge(page)) {
h = page_hstate(page);
} else {
+ spin_unlock_irq(&hugetlb_lock);
start_pfn++;
continue;
}
+ spin_unlock_irq(&hugetlb_lock);
if (!page_count(page)) {
ret = alloc_and_dissolve_huge_page(h, page, &isolate_list);
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2026-11-05 7:02 [PATCH 5.15] mm: replace free hugepage folios after migration Mark Bundschuh
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2026-11-06 22:04 ` [PATCH v2 5.15 0/2] " Mark Bundschuh
2026-11-06 22:04 ` [PATCH v2 5.15 1/2] " Mark Bundschuh
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