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FAILED: patch "[PATCH] mm/ptdump: take the memory hotplug lock inside" failed to apply to 6.1-stable tree

PATCH New [email protected] 2 participants 2 messages Aug 18, 2025 – Aug 19, 2025

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Stable branch Memory management MM core RISC-V +3 more subsystems
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#0 lore raw

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 59305202c67fea50378dcad0cc199dbc13a0e99a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025081859-excess-willfully-0f01@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 59305202c67fea50378dcad0cc199dbc13a0e99a Mon Sep 17 00:00:00 2001
From: Anshuman Khandual <[email protected]>
Date: Fri, 20 Jun 2025 10:54:27 +0530
Subject: [PATCH] mm/ptdump: take the memory hotplug lock inside
ptdump_walk_pgd()

Memory hot remove unmaps and tears down various kernel page table regions as required. The ptdump code can race with concurrent modifications of the kernel page tables. When leaf entries are modified concurrently, the dump code may log stale or inconsistent information for a VA range, but this is otherwise not harmful.

But when intermediate levels of kernel page table are freed, the dump code will continue to use memory that has been freed and potentially reallocated for another purpose. In such cases, the ptdump code may dereference bogus addresses, leading to a number of potential problems.

To avoid the above mentioned race condition, platforms such as arm64, riscv and s390 take memory hotplug lock, while dumping kernel page table via the sysfs interface /sys/kernel/debug/kernel_page_tables.

Similar race condition exists while checking for pages that might have been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in turn calls ptdump_check_wx(). Instead of solving this race condition again, let's just move the memory hotplug lock inside generic ptdump_check_wx() which will benefit both the scenarios.

Drop get_online_mems() and put_online_mems() combination from all existing platform ptdump code paths.

Link https://lkml.kernel.org/r/[email protected] open here
Fixes bbd6ec605c0f ("arm64/mm: Enable memory hot remove")
Signed-off-by Anshuman Khandual <[email protected]>
Acked-by David Hildenbrand <[email protected]>
Reviewed-by Dev Jain <[email protected]>
Acked-by Alexander Gordeev <[email protected]> [s390]
Cc Catalin Marinas <[email protected]>
Cc Will Deacon <[email protected]>
Cc Ryan Roberts <[email protected]>
Cc Paul Walmsley <[email protected]>
Cc Palmer Dabbelt <[email protected]>
Cc Alexander Gordeev <[email protected]>
Cc Gerald Schaefer <[email protected]>
Cc Heiko Carstens <[email protected]>
Cc Vasily Gorbik <[email protected]>
Cc Christian Borntraeger <[email protected]>
Cc Sven Schnelle <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
arch/arm64/mm/ptdump_debugfs.c +0 -3
index 68bf1a125502..1e308328c079 100644
@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/debugfs.h>
-#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 
 #include <asm/ptdump.h>

@@ -9,9 +8,7 @@ static int ptdump_show(struct seq_file *m, void *v)
 {
 	struct ptdump_info *info = m->private;
 
-	get_online_mems();
 	ptdump_walk(m, info);
-	put_online_mems();
 	return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);
arch/riscv/mm/ptdump.c +0 -3
index 32922550a50a..3b51690cc876 100644
@@ -6,7 +6,6 @@
 #include <linux/efi.h>
 #include <linux/init.h>
 #include <linux/debugfs.h>
-#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 #include <linux/ptdump.h>
 

@@ -413,9 +412,7 @@ bool ptdump_check_wx(void)
 
 static int ptdump_show(struct seq_file *m, void *v)
 {
-	get_online_mems();
 	ptdump_walk(m, m->private);
-	put_online_mems();
 
 	return 0;
 }
arch/s390/mm/dump_pagetables.c +0 -2
index ac604b176660..9af2aae0a515 100644
@@ -247,11 +247,9 @@ static int ptdump_show(struct seq_file *m, void *v)
 		.marker = markers,
 	};
 
-	get_online_mems();
 	mutex_lock(&cpa_mutex);
 	ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
 	mutex_unlock(&cpa_mutex);
-	put_online_mems();
 	return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);
mm/ptdump.c +2 -0
index 61a352aa12ed..b600c7f864b8 100644
@@ -176,6 +176,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 {
 	const struct ptdump_range *range = st->range;
 
+	get_online_mems();
 	mmap_write_lock(mm);
 	while (range->start != range->end) {
 		walk_page_range_debug(mm, range->start, range->end,

@@ -183,6 +184,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 		range++;
 	}
 	mmap_write_unlock(mm);
+	put_online_mems();
 
 	/* Flush out the last page */
 	st->note_page_flush(st);
maintainer
#1 lore raw

PATCH 1/1 mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd()

From: Anshuman Khandual <[email protected]>

[ Upstream commit 59305202c67fea50378dcad0cc199dbc13a0e99a ]

Memory hot remove unmaps and tears down various kernel page table regions as required. The ptdump code can race with concurrent modifications of the kernel page tables. When leaf entries are modified concurrently, the dump code may log stale or inconsistent information for a VA range, but this is otherwise not harmful.

But when intermediate levels of kernel page table are freed, the dump code will continue to use memory that has been freed and potentially reallocated for another purpose. In such cases, the ptdump code may dereference bogus addresses, leading to a number of potential problems.

To avoid the above mentioned race condition, platforms such as arm64, riscv and s390 take memory hotplug lock, while dumping kernel page table via the sysfs interface /sys/kernel/debug/kernel_page_tables.

Similar race condition exists while checking for pages that might have been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in turn calls ptdump_check_wx(). Instead of solving this race condition again, let's just move the memory hotplug lock inside generic ptdump_check_wx() which will benefit both the scenarios.

Drop get_online_mems() and put_online_mems() combination from all existing platform ptdump code paths.

Link https://lkml.kernel.org/r/[email protected] open here
Fixes bbd6ec605c0f ("arm64/mm: Enable memory hot remove")
Signed-off-by Anshuman Khandual <[email protected]>
Acked-by David Hildenbrand <[email protected]>
Reviewed-by Dev Jain <[email protected]>
Acked-by Alexander Gordeev <[email protected]> [s390]
Cc Catalin Marinas <[email protected]>
Cc Will Deacon <[email protected]>
Cc Ryan Roberts <[email protected]>
Cc Paul Walmsley <[email protected]>
Cc Palmer Dabbelt <[email protected]>
Cc Alexander Gordeev <[email protected]>
Cc Gerald Schaefer <[email protected]>
Cc Heiko Carstens <[email protected]>
Cc Vasily Gorbik <[email protected]>
Cc Christian Borntraeger <[email protected]>
Cc Sven Schnelle <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Sasha Levin <[email protected]>
---
 arch/arm64/mm/ptdump_debugfs.c | 3 ---
 arch/s390/mm/dump_pagetables.c | 2 --
 mm/ptdump.c                    | 2 ++
 3 files changed, 2 insertions(+), 5 deletions(-)
arch/arm64/mm/ptdump_debugfs.c +0 -3
index 68bf1a125502..1e308328c079 100644
@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/debugfs.h>
-#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 
 #include <asm/ptdump.h>

@@ -9,9 +8,7 @@ static int ptdump_show(struct seq_file *m, void *v)
 {
 	struct ptdump_info *info = m->private;
 
-	get_online_mems();
 	ptdump_walk(m, info);
-	put_online_mems();
 	return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);
arch/s390/mm/dump_pagetables.c +0 -2
index ba5f80268878..65243e1d0c8e 100644
@@ -249,11 +249,9 @@ static int ptdump_show(struct seq_file *m, void *v)
 		.marker = address_markers,
 	};
 
-	get_online_mems();
 	mutex_lock(&cpa_mutex);
 	ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
 	mutex_unlock(&cpa_mutex);
-	put_online_mems();
 	return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);
mm/ptdump.c +2 -0
index 8adab455a68b..8e29b90d6bc3 100644
@@ -152,6 +152,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 {
 	const struct ptdump_range *range = st->range;
 
+	get_online_mems();
 	mmap_write_lock(mm);
 	while (range->start != range->end) {
 		walk_page_range_novma(mm, range->start, range->end,

@@ -159,6 +160,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 		range++;
 	}
 	mmap_write_unlock(mm);
+	put_online_mems();
 
 	/* Flush out the last page */
 	st->note_page(st, 0, -1, 0);
Signature · 1 line
2.50.1