Correct zone boundary handling when resetting pageblock skip hints

PATCH In review Mel Gorman 2 participants 3 messages Mar 27, 2019

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Mel Gorman

author

2019-03-27 08:54 UTC #0 lore raw

PATCH 1/1 Correct zone boundary handling when resetting pageblock skip hints

Mikhail Gavrilo reported the following bug being triggered in a Fedora kernel based on 5.1-rc1 but it is relevant to a vanilla kernel.

kernel: page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
kernel: ------------[ cut here ]------------
kernel: kernel BUG at include/linux/mm.h:1021!
kernel: invalid opcode: 0000 [#1] SMP NOPTI
kernel: CPU: 6 PID: 116 Comm: kswapd0 Tainted: G C 5.1.0-0.rc1.git1.3.fc31.x86_64 #1
kernel: Hardware name: System manufacturer System Product Name/ROG STRIX X470-I GAMING, BIOS 1201 12/07/2018
kernel: RIP: 0010:__reset_isolation_pfn+0x244/0x2b0
kernel: Code: fe 06 e8 0f 8e fc ff 44 0f b6 4c 24 04 48 85 c0 0f 85 dc fe ff ff e9 68 fe ff ff 48 c7 c6 58 b7 2e 8c 4c 89 ff e8 0c 75 00 00 <0f> 0b 48 c7 c6 58 b7 2e 8c e8 fe 74 00 00 0f 0b 48 89 fa 41 b8 01
kernel: RSP: 0018:ffff9e2d03f0fde8 EFLAGS: 00010246
kernel: RAX: 0000000000000034 RBX: 000000000081f380 RCX: ffff8cffbddd6c20
kernel: RDX: 0000000000000000 RSI: 0000000000000006 RDI: ffff8cffbddd6c20
kernel: RBP: 0000000000000001 R08: 0000009898b94613 R09: 0000000000000000
kernel: R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000100000
kernel: R13: 0000000000100000 R14: 0000000000000001 R15: ffffca7de07ce000
kernel: FS: 0000000000000000(0000) GS:ffff8cffbdc00000(0000) knlGS:0000000000000000
kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kernel: CR2: 00007fc1670e9000 CR3: 00000007f5276000 CR4: 00000000003406e0
kernel: Call Trace:

 kernel:  __reset_isolation_suitable+0x62/0x120
 kernel:  reset_isolation_suitable+0x3b/0x40
 kernel:  kswapd+0x147/0x540
 kernel:  ? finish_wait+0x90/0x90
 kernel:  kthread+0x108/0x140
 kernel:  ? balance_pgdat+0x560/0x560
 kernel:  ? kthread_park+0x90/0x90
 kernel:  ret_from_fork+0x27/0x50

He bisected it down to commit e332f741a8dd ("mm, compaction: be selective about what pageblocks to clear skip hints"). The problem is that the patch in question was sloppy with respect to the handling of zone boundaries. In some instances, it was possible for PFNs outside of a zone to be examined and if those were not properly initialised or poisoned then it would trigger the VM_BUG_ON. This patch corrects the zone boundary issues when resetting pageblock skip hints and Mikhail reported that the bug did not trigger after 30 hours of testing.

Fixes e332f741a8dd ("mm, compaction: be selective about what pageblocks to clear skip hints")

Reported-and-tested-by Mikhail Gavrilov <[email protected]>

Signed-off-by Mel Gorman <[email protected]>

---
 mm/compaction.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

mm/compaction.c +17 ~~-10~~

index f171a83707ce..b4930bf93c8a 100644
@@ -242,6 +242,7 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 							bool check_target)
 {
 	struct page *page = pfn_to_online_page(pfn);
+	struct page *block_page;
 	struct page *end_page;
 	unsigned long block_pfn;

@@ -267,20 +268,26 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 	    get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
 		return false;
 
+	/* Ensure the start of the pageblock or zone is online and valid */
+	block_pfn = pageblock_start_pfn(pfn);
+	block_page = pfn_to_online_page(max(block_pfn, zone->zone_start_pfn));
+	if (block_page) {
+		page = block_page;
+		pfn = block_pfn;
+	}
+
+	/* Ensure the end of the pageblock or zone is online and valid */
+	block_pfn += pageblock_nr_pages;
+	block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
+	end_page = pfn_to_online_page(block_pfn);
+	if (!end_page)
+		return false;
+
 	/*
 	 * Only clear the hint if a sample indicates there is either a
 	 * free page or an LRU page in the block. One or other condition
 	 * is necessary for the block to be a migration source/target.
 	 */
-	block_pfn = pageblock_start_pfn(pfn);
-	pfn = max(block_pfn, zone->zone_start_pfn);
-	page = pfn_to_page(pfn);
-	if (zone != page_zone(page))
-		return false;
-	pfn = block_pfn + pageblock_nr_pages;
-	pfn = min(pfn, zone_end_pfn(zone));
-	end_page = pfn_to_page(pfn);
-
 	do {
 		if (pfn_valid_within(pfn)) {
 			if (check_source && PageLRU(page)) {

@@ -309,7 +316,7 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 static void __reset_isolation_suitable(struct zone *zone)
 {
 	unsigned long migrate_pfn = zone->zone_start_pfn;
-	unsigned long free_pfn = zone_end_pfn(zone);
+	unsigned long free_pfn = zone_end_pfn(zone) - 1;
 	unsigned long reset_migrate = free_pfn;
 	unsigned long reset_free = migrate_pfn;
 	bool source_set = false;

Anshuman Khandual

2019-03-27 12:17 UTC #1 lore raw

Quoted 66 lines · Mel Gorman

Mikhail Gavrilo reported the following bug being triggered in a Fedora kernel based on 5.1-rc1 but it is relevant to a vanilla kernel.
kernel: page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
kernel: ------------[ cut here ]------------
kernel: kernel BUG at include/linux/mm.h:1021!
kernel: invalid opcode: 0000 [#1] SMP NOPTI
kernel: CPU: 6 PID: 116 Comm: kswapd0 Tainted: G C 5.1.0-0.rc1.git1.3.fc31.x86_64 #1
kernel: Hardware name: System manufacturer System Product Name/ROG STRIX X470-I GAMING, BIOS 1201 12/07/2018
kernel: RIP: 0010:__reset_isolation_pfn+0x244/0x2b0
kernel: Code: fe 06 e8 0f 8e fc ff 44 0f b6 4c 24 04 48 85 c0 0f 85 dc fe ff ff e9 68 fe ff ff 48 c7 c6 58 b7 2e 8c 4c 89 ff e8 0c 75 00 00 <0f> 0b 48 c7 c6 58 b7 2e 8c e8 fe 74 00 00 0f 0b 48 89 fa 41 b8 01
kernel: RSP: 0018:ffff9e2d03f0fde8 EFLAGS: 00010246
kernel: RAX: 0000000000000034 RBX: 000000000081f380 RCX: ffff8cffbddd6c20
kernel: RDX: 0000000000000000 RSI: 0000000000000006 RDI: ffff8cffbddd6c20
kernel: RBP: 0000000000000001 R08: 0000009898b94613 R09: 0000000000000000
kernel: R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000100000
kernel: R13: 0000000000100000 R14: 0000000000000001 R15: ffffca7de07ce000
kernel: FS: 0000000000000000(0000) GS:ffff8cffbdc00000(0000) knlGS:0000000000000000
kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kernel: CR2: 00007fc1670e9000 CR3: 00000007f5276000 CR4: 00000000003406e0
kernel: Call Trace:
 kernel:  __reset_isolation_suitable+0x62/0x120
 kernel:  reset_isolation_suitable+0x3b/0x40
 kernel:  kswapd+0x147/0x540
 kernel:  ? finish_wait+0x90/0x90
 kernel:  kthread+0x108/0x140
 kernel:  ? balance_pgdat+0x560/0x560
 kernel:  ? kthread_park+0x90/0x90
 kernel:  ret_from_fork+0x27/0x50
He bisected it down to commit e332f741a8dd ("mm, compaction: be selective about what pageblocks to clear skip hints"). The problem is that the patch in question was sloppy with respect to the handling of zone boundaries. In some instances, it was possible for PFNs outside of a zone to be examined and if those were not properly initialised or poisoned then it would trigger the VM_BUG_ON. This patch corrects the zone boundary issues when resetting pageblock skip hints and Mikhail reported that the bug did not trigger after 30 hours of testing.
Fixes e332f741a8dd ("mm, compaction: be selective about what pageblocks to clear skip hints")
Reported-and-tested-by Mikhail Gavrilov <[email protected]>
Signed-off-by Mel Gorman <[email protected]>
---
 mm/compaction.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)
mm/compaction.c +5 -0
index f171a83707ce..b4930bf93c8a 100644
@@ -242,6 +242,7 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 							bool check_target)
 {
 	struct page *page = pfn_to_online_page(pfn);
+	struct page *block_page;
 	struct page *end_page;
 	unsigned long block_pfn;
 
@@ -267,20 +268,26 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 	    get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
 		return false;
 
+	/* Ensure the start of the pageblock or zone is online and valid */
+	block_pfn = pageblock_start_pfn(pfn);
+	block_page = pfn_to_online_page(max(block_pfn, zone->zone_start_pfn));
+	if (block_page) {

mm/compaction.c __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source, · line 284

Quoted 10 lines

mm/compaction.c +10 -0

+		page = block_page;
+		pfn = block_pfn;
+	}
+
+	/* Ensure the end of the pageblock or zone is online and valid */
+	block_pfn += pageblock_nr_pages;
+	block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
+	end_page = pfn_to_online_page(block_pfn);
+	if (!end_page)
+		return false;

Should not we check zone against page_zone() from both start and end page here.

Mel Gorman

author

2019-03-27 12:45 UTC #2 lore raw

Quoted 4 lines · Anshuman Khandual

Quoted 4 lines

mm/compaction.c +0 -0

@@ -267,20 +268,26 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 	    get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
 		return false;

Quoted 16 lines

Quoted 4 lines
mm/compaction.c +4 -0
+	/* Ensure the start of the pageblock or zone is online and valid */
+	block_pfn = pageblock_start_pfn(pfn);
+	block_page = pfn_to_online_page(max(block_pfn, zone->zone_start_pfn));
+	if (block_page) {
mm/compaction.c __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source, · line 284
Quoted 10 lines
mm/compaction.c +10 -0
+		page = block_page;
+		pfn = block_pfn;
+	}
+
+	/* Ensure the end of the pageblock or zone is online and valid */
+	block_pfn += pageblock_nr_pages;
+	block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
+	end_page = pfn_to_online_page(block_pfn);
+	if (!end_page)
+		return false;
Should not we check zone against page_zone() from both start and end page here.

The lower address has the max(block_pfn, zone->zone_start_pfn) and the upper address has the min(block_pfn, zone_end_pfn(zone) - 1) check to keep the PFN within the zone boundary.

Signature · 2 lines

Mel Gorman
SUSE Labs