Patch "mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled" has been added to the 5.4-stable tree

DISCUSSION Vlastimil Babka 2 participants 3 messages Mar 9, 2020 1 message not in the archive Stable branch

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Vlastimil Babka

author

2020-03-09 20:11 UTC #1 lore raw

Quoted 111 lines · On 3/9/2020 8:22 PM, [email protected] wrote:

This is a note to let you know that I've just added the patch titled
mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
From c87cbc1f007c4b46165f05ceca04e1973cda0b9c Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <[email protected]>
Date: Thu, 5 Mar 2020 22:28:42 -0800
Subject: mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled
From: Vlastimil Babka <[email protected]>
commit c87cbc1f007c4b46165f05ceca04e1973cda0b9c upstream.
Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") fixed memory hotplug with debug_pagealloc enabled, where onlining a page goes through page freeing, which removes the direct mapping. Some arches don't like when the page is not mapped in the first place, so generic_online_page() maps it first. This is somewhat wasteful, but better than special casing page freeing fast paths.
The commit however missed that DEBUG_PAGEALLOC configured doesn't mean it's actually enabled. One has to test debug_pagealloc_enabled() since 031bc5743f15 ("mm/debug-pagealloc: make debug-pagealloc boottime configurable"), or alternatively debug_pagealloc_enabled_static() since 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early"), but this is not done.
As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled will crash:
Unable to handle kernel pointer dereference in virtual kernel address space
Failing address: 0000000000000000 TEID: 0000000000000483
Fault in home space mode while using kernel ASCE.
AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d
Oops: 0004 ilc:2 [#1] SMP
CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased)
Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188)
R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 0000000000000001 0000000000000000 0000000000000002 0000000000000100 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3
Quoted 1 line
0000001ecd281b9e: 94fb5006 ni 6(%r5),251
0000001ecd281ba2: 41505008 la %r5,8(%r5) 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e 0000001ecd281bac: 1a07 ar %r0,%r7 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e
Call Trace:
[<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188
[<0000001ecd4d9516>] online_pages_range+0xf6/0x128
[<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8
[<0000001ecda28aae>] online_pages+0x2fe/0x3f0
[<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0
[<0000001ecd7add42>] device_online+0x5a/0xc8
[<0000001ecd7d0430>] state_store+0x88/0x118
[<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200
[<0000001ecd5064b6>] vfs_write+0x176/0x1e0
[<0000001ecd50676a>] ksys_write+0xa2/0x100
[<0000001ecda315d4>] system_call+0xd8/0x2c8
Fix this by checking debug_pagealloc_enabled_static() before calling kernel_map_pages(). Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead. Also add comments.
Fixes cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC")
Reported-by Gerald Schaefer <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Vlastimil Babka <[email protected]>
Reviewed-by David Hildenbrand <[email protected]>
Cc <[email protected]>
Cc Joonsoo Kim <[email protected]>
Cc Qian Cai <[email protected]>
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 include/linux/mm.h  |    4 ++++
 mm/memory_hotplug.c |    8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)
include/linux/mm.h +4 -0
@@ -2695,6 +2695,10 @@ static inline bool debug_pagealloc_enabl
 #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
+/*
+ * When called in DEBUG_PAGEALLOC context, the call should most likely be
+ * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
+ */
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable)
 {

mm/memory_hotplug.c EXPORT_SYMBOL_GPL(__online_page_free); · line 606

Quoted 10 lines

mm/memory_hotplug.c +6 -1

@@ -598,7 +598,13 @@ EXPORT_SYMBOL_GPL(__online_page_free);
 
 static void generic_online_page(struct page *page, unsigned int order)
 {
-	kernel_map_pages(page, 1 << order, 1);
+	/*
+	 * Freeing the page with debug_pagealloc enabled will try to unmap it,
+	 * so we should map it first. This is better than introducing a special
+	 * case in page freeing fast path.
+	 */
+	if (debug_pagealloc_enabled_static())

Won't build on 5.4, see in changelog "Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead."

Quoted 12 lines

mm/memory_hotplug.c +1 -0
+		kernel_map_pages(page, 1 << order, 1);
 	__free_pages_core(page, order);
 	totalram_pages_add(1UL << order);
 #ifdef CONFIG_HIGHMEM
Patches currently in stable-queue which might be from [email protected] are
queue-5.4/mm-numa-fix-bad-pmd-by-atomically-check-for-pmd_trans_huge-when-marking-page-tables-prot_numa.patch queue-5.4/mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch queue-5.4/mm-fix-possible-pmd-dirty-bit-lost-in-set_pmd_migration_entry.patch

Greg KH

maintainer

2020-03-09 20:21 UTC #2 lore raw

Quoted 113 lines · Vlastimil Babka

Quoted 112 lines · On 3/9/2020 8:22 PM, [email protected] wrote:
This is a note to let you know that I've just added the patch titled
mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
From c87cbc1f007c4b46165f05ceca04e1973cda0b9c Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <[email protected]>
Date: Thu, 5 Mar 2020 22:28:42 -0800
Subject: mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled
From: Vlastimil Babka <[email protected]>
commit c87cbc1f007c4b46165f05ceca04e1973cda0b9c upstream.
Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") fixed memory hotplug with debug_pagealloc enabled, where onlining a page goes through page freeing, which removes the direct mapping. Some arches don't like when the page is not mapped in the first place, so generic_online_page() maps it first. This is somewhat wasteful, but better than special casing page freeing fast paths.
The commit however missed that DEBUG_PAGEALLOC configured doesn't mean it's actually enabled. One has to test debug_pagealloc_enabled() since 031bc5743f15 ("mm/debug-pagealloc: make debug-pagealloc boottime configurable"), or alternatively debug_pagealloc_enabled_static() since 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early"), but this is not done.
As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled will crash:
Unable to handle kernel pointer dereference in virtual kernel address space
Failing address: 0000000000000000 TEID: 0000000000000483
Fault in home space mode while using kernel ASCE.
AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d
Oops: 0004 ilc:2 [#1] SMP
CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased)
Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188)
R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 0000000000000001 0000000000000000 0000000000000002 0000000000000100 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3
Quoted 1 line
0000001ecd281b9e: 94fb5006 ni 6(%r5),251
0000001ecd281ba2: 41505008 la %r5,8(%r5) 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e 0000001ecd281bac: 1a07 ar %r0,%r7 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e
Call Trace:
[<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188
[<0000001ecd4d9516>] online_pages_range+0xf6/0x128
[<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8
[<0000001ecda28aae>] online_pages+0x2fe/0x3f0
[<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0
[<0000001ecd7add42>] device_online+0x5a/0xc8
[<0000001ecd7d0430>] state_store+0x88/0x118
[<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200
[<0000001ecd5064b6>] vfs_write+0x176/0x1e0
[<0000001ecd50676a>] ksys_write+0xa2/0x100
[<0000001ecda315d4>] system_call+0xd8/0x2c8
Fix this by checking debug_pagealloc_enabled_static() before calling kernel_map_pages(). Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead. Also add comments.
Fixes cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC")
Reported-by Gerald Schaefer <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Vlastimil Babka <[email protected]>
Reviewed-by David Hildenbrand <[email protected]>
Cc <[email protected]>
Cc Joonsoo Kim <[email protected]>
Cc Qian Cai <[email protected]>
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 include/linux/mm.h  |    4 ++++
 mm/memory_hotplug.c |    8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)
include/linux/mm.h +4 -0
@@ -2695,6 +2695,10 @@ static inline bool debug_pagealloc_enabl
 #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
+/*
+ * When called in DEBUG_PAGEALLOC context, the call should most likely be
+ * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
+ */
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable)
 {
mm/memory_hotplug.c +0 -0
@@ -598,7 +598,13 @@ EXPORT_SYMBOL_GPL(__online_page_free);
 

Quoted 12 lines

mm/memory_hotplug.c EXPORT_SYMBOL_GPL(__online_page_free); · line 606
Quoted 9 lines
mm/memory_hotplug.c +6 -1
 static void generic_online_page(struct page *page, unsigned int order)
 {
-	kernel_map_pages(page, 1 << order, 1);
+	/*
+	 * Freeing the page with debug_pagealloc enabled will try to unmap it,
+	 * so we should map it first. This is better than introducing a special
+	 * case in page freeing fast path.
+	 */
+	if (debug_pagealloc_enabled_static())
Won't build on 5.4, see in changelog "Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead."

Builds just fine for me here, are you _sure_ 5.4.y doesn't work?

5.4.14 got debug_pagealloc_enabled_static() through the backport of 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early") which you wrote :)

Now if it still needs to be changed, let me know and I will do so.

thanks,

greg k-h

Vlastimil Babka

author

2020-03-09 20:52 UTC #3 lore raw

Quoted 18 lines · Greg KH

Quoted 4 lines · Vlastimil Babka
Quoted 4 lines
mm/memory_hotplug.c +0 -0
@@ -598,7 +598,13 @@ EXPORT_SYMBOL_GPL(__online_page_free);
 
Quoted 12 lines
mm/memory_hotplug.c EXPORT_SYMBOL_GPL(__online_page_free); · line 606
Quoted 9 lines
mm/memory_hotplug.c +6 -1
 static void generic_online_page(struct page *page, unsigned int order)
 {
-	kernel_map_pages(page, 1 << order, 1);
+	/*
+	 * Freeing the page with debug_pagealloc enabled will try to unmap it,
+	 * so we should map it first. This is better than introducing a special
+	 * case in page freeing fast path.
+	 */
+	if (debug_pagealloc_enabled_static())
Won't build on 5.4, see in changelog "Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead."

Quoted 5 lines

Builds just fine for me here, are you _sure_ 5.4.y doesn't work?
5.4.14 got debug_pagealloc_enabled_static() through the backport of 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early") which you wrote :)

Ah ok, didn't realize that, I probably only checked the mainline :)

Quoted 1 line

Now if it still needs to be changed, let me know and I will do so.

Nothing needs to change then, sorry for the noise.

Quoted 4 lines

thanks,
greg k-h