Isolated balloon pages can wrongly end up in LRU lists when migrate_pages()
finishes its round without draining all the isolated page list. The same issue
can happen when reclaim_clean_pages_from_list() tries to reclaim pages from an
isolated page list, before migration, in the CMA path. Such balloon page leak
opens a race window against LRU lists shrinkers that leads us to the following
kernel panic:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
IP: [<ffffffff810c2625>] shrink_page_list+0x24e/0x897
PGD 3cda2067 PUD 3d713067 PMD 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 340 Comm: kswapd0 Not tainted 3.12.0-rc1-22626-g4367597 #87
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff88003d920ee0 ti: ffff88003da48000 task.ti: ffff88003da48000
RIP: 0010:[<ffffffff810c2625>] [<ffffffff810c2625>] shrink_page_list+0x24e/0x897
RSP: 0000:ffff88003da499b8 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff88003e82bd60 RCX: 00000000000657d5
RDX: 0000000000000000 RSI: 000000000000031f RDI: ffff88003e82bd40
RBP: ffff88003da49ab0 R08: 0000000000000001 R09: 0000000081121a45
R10: ffffffff81121a45 R11: ffff88003c4a9a28 R12: ffff88003e82bd40
R13: ffff88003da0e800 R14: 0000000000000001 R15: ffff88003da49d58
FS: 0000000000000000(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000067d9000 CR3: 000000003ace5000 CR4: 00000000000407b0
Stack:
ffff88003d920ee0 ffff88003d920ee0 ffff88003da49a50 ffff88003da49a40
ffff88003da49b18 ffff88003da49b08 0000000000a499e0 ffffffff81667fc0
0000000000000000 0000000000000000 0000000000000000 0000000000000000
Call Trace:
[<ffffffff8107507f>] ? lock_release+0x188/0x1d7
[<ffffffff810c31f8>] shrink_inactive_list+0x240/0x3de
[<ffffffff810c3a3b>] shrink_lruvec+0x3e0/0x566
[<ffffffff810734c4>] ? __lock_is_held+0x38/0x50
[<ffffffff810c3c55>] __shrink_zone+0x94/0x178
[<ffffffff810c3d73>] shrink_zone+0x3a/0x82
[<ffffffff810c4818>] balance_pgdat+0x32a/0x4c2
[<ffffffff810c4ca0>] kswapd+0x2f0/0x372
[<ffffffff8104fb93>] ? abort_exclusive_wait+0x8b/0x8b
[<ffffffff810c49b0>] ? balance_pgdat+0x4c2/0x4c2
[<ffffffff8104ef73>] kthread+0xa2/0xaa
[<ffffffff8104eed1>] ? __kthread_parkme+0x65/0x65
[<ffffffff81364f6c>] ret_from_fork+0x7c/0xb0
[<ffffffff8104eed1>] ? __kthread_parkme+0x65/0x65
Code: 80 7d 8f 01 48 83 95 68 ff ff ff 00 4c 89 e7 e8 5a 7b 00 00 48 85 c0 49 89 c5 75 08 80 7d 8f 00 74 3e eb 31 48 8b 80 18 01 00 00 <48> 8b 74 0d 48 8b 78 30 be 02 00 00 00 ff d2 eb
RIP [<ffffffff810c2625>] shrink_page_list+0x24e/0x897
RSP <ffff88003da499b8>
CR2: 0000000000000028
---[ end trace 703d2451af6ffbfd ]---
Kernel panic - not syncing: Fatal exception
This patch fixes the issue, by assuring the proper tests are made at
putback_movable_pages() & reclaim_clean_pages_from_list() to avoid
isolated balloon pages being wrongly reinserted in LRU lists.
Reported-and-tested-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
---
include/linux/balloon_compaction.h | 25 +++++++++++++++++++++++++
mm/migrate.c | 2 +-
mm/vmscan.c | 4 +++-
3 files changed, 29 insertions(+), 2 deletions(-)
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index f7f1d71..b5f3ec0 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -159,6 +159,26 @@ static inline bool balloon_page_movable(struct page *page)
}
/*
+ * isolated_balloon_page - identify an isolated balloon page on private
+ * compaction/migration page lists.
+ *
+ * After a compaction thread isolates a balloon page for migration, it raises
+ * the page refcount to avoid concurrent compaction threads on re-isolating the
+ * same page. For that reason putback_movable_pages(), or other routines
+ * that need to identify isolated balloon pages on private pagelists, cannot
+ * rely on balloon_page_movable() to accomplish the task.
+ */
+static inline bool isolated_balloon_page(struct page *page)
+{
+ /* Already isolated balloon pages, by default, have a raised refcount */
+ if (page_flags_cleared(page) && !page_mapped(page) &&
+ page_count(page) >= 2)
+ return __is_movable_balloon_page(page);
+
+ return false;
+}
+
+/*
* balloon_page_insert - insert a page into the balloon's page list and make
* the page->mapping assignment accordingly.
* @page : page to be assigned as a 'balloon page'
@@ -243,6 +263,11 @@ static inline bool balloon_page_movable(struct page *page)
return false;
}
+static inline bool isolated_balloon_page(struct page *page)
+{
+ return false;
+}
+
static inline bool balloon_page_isolate(struct page *page)
{
return false;
diff --git a/mm/migrate.c b/mm/migrate.c
index 9c8d5f5..a26bccd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -107,7 +107,7 @@ void putback_movable_pages(struct list_head *l)
list_del(&page->lru);
dec_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
- if (unlikely(balloon_page_movable(page)))
+ if (unlikely(isolated_balloon_page(page)))
balloon_page_putback(page);
else
putback_lru_page(page);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index beb3577..53f2f82 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -48,6 +48,7 @@
#include <asm/div64.h>
#include <linux/swapops.h>
+#include <linux/balloon_compaction.h>
#include "internal.h"
@@ -1113,7 +1114,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
LIST_HEAD(clean_pages);
list_for_each_entry_safe(page, next, page_list, lru) {
- if (page_is_file_cache(page) && !PageDirty(page)) {
+ if (page_is_file_cache(page) && !PageDirty(page) &&
+ !isolated_balloon_page(page)) {
ClearPageActive(page);
list_move(&page->lru, &clean_pages);
}
--
1.8.3.1
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