The patch titled
Subject: mm/ksm: fix incorrect KSM counter handling in mm_struct during fork
has been added to the -mm mm-unstable branch. Its filename is
mm-ksm-fix-incorrect-ksm-counter-handling-in-mm_struct-during-fork.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patche…
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Donet Tom <donettom(a)linux.ibm.com>
Subject: mm/ksm: fix incorrect KSM counter handling in mm_struct during fork
Date: Wed, 24 Sep 2025 00:16:59 +0530
Patch series "mm/ksm: Fix incorrect accounting of KSM counters during
fork", v3.
The first patch in this series fixes the incorrect accounting of KSM
counters such as ksm_merging_pages, ksm_rmap_items, and the global
ksm_zero_pages during fork.
The following patch add a selftest to verify the ksm_merging_pages counter
was updated correctly during fork.
Test Results
============
Without the first patch
-----------------------
# [RUN] test_fork_ksm_merging_page_count
not ok 10 ksm_merging_page in child: 32
With the first patch
--------------------
# [RUN] test_fork_ksm_merging_page_count
ok 10 ksm_merging_pages is not inherited after fork
This patch (of 2):
Currently, the KSM-related counters in `mm_struct`, such as
`ksm_merging_pages`, `ksm_rmap_items`, and `ksm_zero_pages`, are inherited
by the child process during fork. This results in inconsistent
accounting.
When a process uses KSM, identical pages are merged and an rmap item is
created for each merged page. The `ksm_merging_pages` and
`ksm_rmap_items` counters are updated accordingly. However, after a fork,
these counters are copied to the child while the corresponding rmap items
are not. As a result, when the child later triggers an unmerge, there are
no rmap items present in the child, so the counters remain stale, leading
to incorrect accounting.
A similar issue exists with `ksm_zero_pages`, which maintains both a
global counter and a per-process counter. During fork, the per-process
counter is inherited by the child, but the global counter is not
incremented. Since the child also references zero pages, the global
counter should be updated as well. Otherwise, during zero-page unmerge,
both the global and per-process counters are decremented, causing the
global counter to become inconsistent.
To fix this, ksm_merging_pages and ksm_rmap_items are reset to 0 during
fork, and the global ksm_zero_pages counter is updated with the
per-process ksm_zero_pages value inherited by the child. This ensures
that KSM statistics remain accurate and reflect the activity of each
process correctly.
Link: https://lkml.kernel.org/r/cover.1758648700.git.donettom@linux.ibm.com
Link: https://lkml.kernel.org/r/7b9870eb67ccc0d79593940d9dbd4a0b39b5d396.17586487…
Fixes: 7609385337a4 ("ksm: count ksm merging pages for each process")
Fixes: cb4df4cae4f2 ("ksm: count allocated ksm rmap_items for each process")
Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM")
Signed-off-by: Donet Tom <donettom(a)linux.ibm.com>
Reviewed-by: Chengming Zhou <chengming.zhou(a)linux.dev>
Acked-by: David Hildenbrand <david(a)redhat.com>
Cc: Aboorva Devarajan <aboorvad(a)linux.ibm.com>
Cc: David Hildenbrand <david(a)redhat.com>
Cc: Donet Tom <donettom(a)linux.ibm.com>
Cc: "Ritesh Harjani (IBM)" <ritesh.list(a)gmail.com>
Cc: Wei Yang <richard.weiyang(a)gmail.com>
Cc: xu xin <xu.xin16(a)zte.com.cn>
Cc: <stable(a)vger.kernel.org> [6.6+]
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
include/linux/ksm.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/include/linux/ksm.h~mm-ksm-fix-incorrect-ksm-counter-handling-in-mm_struct-during-fork
+++ a/include/linux/ksm.h
@@ -56,8 +56,14 @@ static inline long mm_ksm_zero_pages(str
static inline void ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
/* Adding mm to ksm is best effort on fork. */
- if (mm_flags_test(MMF_VM_MERGEABLE, oldmm))
+ if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) {
+ long nr_ksm_zero_pages = atomic_long_read(&mm->ksm_zero_pages);
+
+ mm->ksm_merging_pages = 0;
+ mm->ksm_rmap_items = 0;
+ atomic_long_add(nr_ksm_zero_pages, &ksm_zero_pages);
__ksm_enter(mm);
+ }
}
static inline int ksm_execve(struct mm_struct *mm)
_
Patches currently in -mm which might be from donettom(a)linux.ibm.com are
drivers-base-node-fix-double-free-in-register_one_node.patch
mm-ksm-fix-incorrect-ksm-counter-handling-in-mm_struct-during-fork.patch
selftests-mm-added-fork-inheritance-test-for-ksm_merging_pages-counter.patch
devm_kcalloc() may fail. ndtest_probe() allocates three DMA address
arrays (dcr_dma, label_dma, dimm_dma) and later unconditionally uses
them in ndtest_nvdimm_init(), which can lead to a NULL pointer
dereference under low-memory conditions.
Check all three allocations and return -ENOMEM if any allocation fails.
Do not emit an extra error message since the allocator already warns on
allocation failure.
Fixes: 9399ab61ad82 ("ndtest: Add dimms to the two buses")
Cc: stable(a)vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244(a)gmail.com>
---
Changes in v2:
- Drop pr_err() on allocation failure; only NULL-check and return -ENOMEM.
- No other changes.
---
tools/testing/nvdimm/test/ndtest.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/tools/testing/nvdimm/test/ndtest.c b/tools/testing/nvdimm/test/ndtest.c
index 68a064ce598c..abdbe0c1cb63 100644
--- a/tools/testing/nvdimm/test/ndtest.c
+++ b/tools/testing/nvdimm/test/ndtest.c
@@ -855,6 +855,9 @@ static int ndtest_probe(struct platform_device *pdev)
p->dimm_dma = devm_kcalloc(&p->pdev.dev, NUM_DCR,
sizeof(dma_addr_t), GFP_KERNEL);
+ if (!p->dcr_dma || !p->label_dma || !p->dimm_dma)
+ return -ENOMEM;
+
rc = ndtest_nvdimm_init(p);
if (rc)
goto err;
--
2.43.0
Currently, the KSM-related counters in `mm_struct`, such as
`ksm_merging_pages`, `ksm_rmap_items`, and `ksm_zero_pages`, are
inherited by the child process during fork. This results in inconsistent
accounting.
When a process uses KSM, identical pages are merged and an rmap item is
created for each merged page. The `ksm_merging_pages` and
`ksm_rmap_items` counters are updated accordingly. However, after a
fork, these counters are copied to the child while the corresponding
rmap items are not. As a result, when the child later triggers an
unmerge, there are no rmap items present in the child, so the counters
remain stale, leading to incorrect accounting.
A similar issue exists with `ksm_zero_pages`, which maintains both a
global counter and a per-process counter. During fork, the per-process
counter is inherited by the child, but the global counter is not
incremented. Since the child also references zero pages, the global
counter should be updated as well. Otherwise, during zero-page unmerge,
both the global and per-process counters are decremented, causing the
global counter to become inconsistent.
To fix this, ksm_merging_pages and ksm_rmap_items are reset to 0
during fork, and the global ksm_zero_pages counter is updated with the
per-process ksm_zero_pages value inherited by the child. This ensures
that KSM statistics remain accurate and reflect the activity of each
process correctly.
Fixes: 7609385337a4 ("ksm: count ksm merging pages for each process")
Fixes: cb4df4cae4f2 ("ksm: count allocated ksm rmap_items for each process")
Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM")
cc: stable(a)vger.kernel.org # v6.6
Reviewed-by: Chengming Zhou <chengming.zhou(a)linux.dev>
Acked-by: David Hildenbrand <david(a)redhat.com>
Signed-off-by: Donet Tom <donettom(a)linux.ibm.com>
---
include/linux/ksm.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 22e67ca7cba3..067538fc4d58 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -56,8 +56,14 @@ static inline long mm_ksm_zero_pages(struct mm_struct *mm)
static inline void ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
/* Adding mm to ksm is best effort on fork. */
- if (mm_flags_test(MMF_VM_MERGEABLE, oldmm))
+ if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) {
+ long nr_ksm_zero_pages = atomic_long_read(&mm->ksm_zero_pages);
+
+ mm->ksm_merging_pages = 0;
+ mm->ksm_rmap_items = 0;
+ atomic_long_add(nr_ksm_zero_pages, &ksm_zero_pages);
__ksm_enter(mm);
+ }
}
static inline int ksm_execve(struct mm_struct *mm)
--
2.51.0
The Mediatek DRM driver allocates private data for components without a
platform driver but as the lifetime is tied to each component device,
the memory is never freed.
Tie the allocation lifetime to the DRM platform device so that the
memory is released on probe failure (e.g. probe deferral) and when the
driver is unbound.
Fixes: c0d36de868a6 ("drm/mediatek: Move clk info from struct mtk_ddp_comp to sub driver private data")
Cc: stable(a)vger.kernel.org # 5.12
Cc: CK Hu <ck.hu(a)mediatek.com>
Signed-off-by: Johan Hovold <johan(a)kernel.org>
---
drivers/gpu/drm/mediatek/mtk_ddp_comp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_ddp_comp.c b/drivers/gpu/drm/mediatek/mtk_ddp_comp.c
index 0264017806ad..31d67a131c50 100644
--- a/drivers/gpu/drm/mediatek/mtk_ddp_comp.c
+++ b/drivers/gpu/drm/mediatek/mtk_ddp_comp.c
@@ -671,7 +671,7 @@ int mtk_ddp_comp_init(struct device *dev, struct device_node *node, struct mtk_d
type == MTK_DSI)
return 0;
- priv = devm_kzalloc(comp->dev, sizeof(*priv), GFP_KERNEL);
+ priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
--
2.49.1