[PATCH] mm: fix a race scenario in folio_isolate_lru
From: zhaoyang.huang
Date: Thu Mar 14 2024 - 04:40:15 EST
From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
Panic[1] reported which is caused by lruvec->list break. Fix the race
between folio_isolate_lru and release_pages.
race condition:
release_pages could meet a non-refered folio which escaped from being
deleted from LRU but add to another list_head
#0 folio_isolate_lru #1 release_pages
if (folio_test_clear_lru())
if (folio_put_testzero())
if (!folio_test_lru())
<failed to delete folio from LRU>
folio_get(folio)
list_add(&folio->lru,)
list_del(&folio->lru,)
fix action 1:
have folio_get prior to folio_test_clear_lru is not enough as there
could be concurrent folio_put(filemap_remove_folios) to make
release_pages pass refcnt check and failed in delete from LRU
#0 folio_isolate_lru #1 release_pages
folio_get(folio)
if (folio_test_clear_lru())
if (folio_put_testzero())
if (!folio_test_lru())
<failed to delete folio from LRU>
list_add(&folio->lru,)
list_del(&folio->lru,)
fix action 2:
folio_test_clear_lru should be considered as part of critical section of
lruvec which require be within lruvec->lock.
#0 folio_isolate_lru #1 release_pages
spin_lock(lruvec->lock)
folio_get(folio)
if (folio_test_clear_lru())
list_del(&folio->lru,)
<delete folio from LRU>
spin_unlock(lruvec->lock) spin_lock(lruvec->lock)
if (folio_put_testzero())
if (!folio_test_lru())
list_add(&folio->lru,)
[1]
[ 37.562326] pc : __list_del_entry_valid_or_report+0xec/0xf0
[ 37.562344] lr : __list_del_entry_valid_or_report+0xec/0xf0
[ 37.562351] sp : ffffffc085953990
[ 37.562355] x29: ffffffc0859539d0 x28: ffffffc082144000 x27: 000000000000000f
[ 37.562367] x26: 000000000000000d x25: 000000000000000d x24: 00000000ffffffff
[ 37.562377] x23: ffffffc085953a08 x22: ffffff8080389000 x21: ffffff8080389000
[ 37.562388] x20: fffffffe05c54180 x19: ffffffc085953b30 x18: ffffffc085989098
[ 37.562399] x17: 20747562202c3838 x16: ffffffffffffffff x15: 0000000000000004
[ 37.562409] x14: ffffff8176980000 x13: 0000000000007fff x12: 0000000000000003
[ 37.562420] x11: 00000000ffff7fff x10: ffffffc0820f51c4 x9 : 53b71233d5d50e00
[ 37.562431] x8 : 53b71233d5d50e00 x7 : ffffffc081161ff0 x6 : 0000000000000000
[ 37.562441] x5 : 0000000000000001 x4 : 0000000000000001 x3 : 0000000000000000
[ 37.562451] x2 : ffffff817f2c4178 x1 : ffffff817f2b71c8 x0 : 000000000000006d
[ 37.562461] Call trace:
[ 37.562465] __list_del_entry_valid_or_report+0xec/0xf0
[ 37.562472] release_pages+0x410/0x4c0
[ 37.562482] __folio_batch_release+0x34/0x4c
[ 37.562490] truncate_inode_pages_range+0x368/0x63c
[ 37.562497] truncate_inode_pages+0x14/0x24
[ 37.562504] blkdev_flush_mapping+0x60/0x120
[ 37.562513] blkdev_put+0x114/0x298
[ 37.562520] blkdev_release+0x28/0x40
[ 37.562526] __fput+0xf8/0x2a8
[ 37.562533] ____fput+0x10/0x20
[ 37.562539] task_work_run+0xc4/0xec
[ 37.562546] do_exit+0x32c/0xa3c
[ 37.562554] do_group_exit+0x98/0x9c
[ 37.562561] __arm64_sys_exit_group+0x18/0x1c
[ 37.562568] invoke_syscall+0x58/0x114
[ 37.562575] el0_svc_common+0xac/0xe0
[ 37.562582] do_el0_svc+0x1c/0x28
[ 37.562588] el0_svc+0x50/0xe4
[ 37.562593] el0t_64_sync_handler+0x68/0xbc
[ 37.562599] el0t_64_sync+0x1a8/0x1ac
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
mm/swap.c | 25 +++++++++++++++++--------
mm/vmscan.c | 25 +++++++++++++++++++------
2 files changed, 36 insertions(+), 14 deletions(-)
diff --git a/mm/swap.c b/mm/swap.c
index cd8f0150ba3a..287cf7379927 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -968,6 +968,7 @@ void release_pages(release_pages_arg arg, int nr)
for (i = 0; i < nr; i++) {
struct folio *folio;
+ struct lruvec *prev_lruvec;
/* Turn any of the argument types into a folio */
folio = page_folio(encoded_page_ptr(encoded[i]));
@@ -996,9 +997,24 @@ void release_pages(release_pages_arg arg, int nr)
free_zone_device_page(&folio->page);
continue;
}
+ /*
+ * lruvec->lock need to be prior to folio_put_testzero to
+ * prevent race with folio_isolate_lru
+ */
+ prev_lruvec = lruvec;
+ lruvec = folio_lruvec_relock_irqsave(folio, lruvec,
+ &flags);
+
+ if (prev_lruvec != lruvec)
+ lock_batch = 0;
- if (!folio_put_testzero(folio))
+ if (!folio_put_testzero(folio)) {
+ if (lruvec) {
+ unlock_page_lruvec_irqrestore(lruvec, flags);
+ lruvec = NULL;
+ }
continue;
+ }
if (folio_test_large(folio)) {
if (lruvec) {
@@ -1010,13 +1026,6 @@ void release_pages(release_pages_arg arg, int nr)
}
if (folio_test_lru(folio)) {
- struct lruvec *prev_lruvec = lruvec;
-
- lruvec = folio_lruvec_relock_irqsave(folio, lruvec,
- &flags);
- if (prev_lruvec != lruvec)
- lock_batch = 0;
-
lruvec_del_folio(lruvec, folio);
__folio_clear_lru_flags(folio);
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4255619a1a31..13a4a716c67a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1721,18 +1721,31 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
bool folio_isolate_lru(struct folio *folio)
{
bool ret = false;
+ struct lruvec *lruvec;
VM_BUG_ON_FOLIO(!folio_ref_count(folio), folio);
- if (folio_test_clear_lru(folio)) {
- struct lruvec *lruvec;
+ /*
+ * The folio_get needs to be prior to clear lru for list integrity.
+ * Otherwise:
+ * #0 folio_isolate_lru #1 release_pages
+ * if (folio_test_clear_lru())
+ * if (folio_put_testzero())
+ * if (!folio_test_lru())
+ * <failed to del folio from LRU>
+ * folio_get(folio)
+ * list_add(&folio->lru,)
+ * list_del(&folio->lru,)
+ */
+ lruvec = folio_lruvec_lock_irq(folio);
+ folio_get(folio);
- folio_get(folio);
- lruvec = folio_lruvec_lock_irq(folio);
+ if (folio_test_clear_lru(folio)) {
lruvec_del_folio(lruvec, folio);
- unlock_page_lruvec_irq(lruvec);
ret = true;
- }
+ } else
+ folio_put(folio);
+ unlock_page_lruvec_irq(lruvec);
return ret;
}
--
2.25.1