[PATCH] mm: fix unevictable page reclaim when calling madvise_pageout

[zhong jiang <zhongjiang@huawei.com>]

Recently, I hit the following issue when running in the upstream.

kernel BUG at mm/vmscan.c:1521!
invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 PID: 23385 Comm: syz-executor.6 Not tainted 5.4.0-rc4+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
RIP: 0010:shrink_page_list+0x12b6/0x3530 mm/vmscan.c:1521
Code: de f5 ff ff e8 ab 79 eb ff 4c 89 f7 e8 43 33 0d 00 e9 cc f5 ff ff e8 99 79 eb ff 48 c7 c6 a0 34 2b a0 4c 89 f7 e8 1a 4d 05 00 <0f> 0b e8 83 79 eb ff 48 89 d8 48 c1 e8 03 42 80 3c 38 00 0f 85 74
RSP: 0018:ffff88819a3df5a0 EFLAGS: 00010286
RAX: 0000000000040000 RBX: ffffea00061c3980 RCX: ffffffff814fba36
RDX: 00000000000056f7 RSI: ffffc9000c02c000 RDI: ffff8881f70268cc
RBP: ffff88819a3df898 R08: ffffed103ee05de0 R09: ffffed103ee05de0
R10: 0000000000000001 R11: ffffed103ee05ddf R12: ffff88819a3df6f0
R13: ffff88819a3df6f0 R14: ffffea00061c3980 R15: dffffc0000000000
FS:  00007f21b9d8e700(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2d621000 CR3: 00000001c8c46004 CR4: 00000000007606f0
DR0: 0000000020000140 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
PKRU: 55555554
Call Trace:
 reclaim_pages+0x499/0x800 mm/vmscan.c:2188
 madvise_cold_or_pageout_pte_range+0x58a/0x710 mm/madvise.c:453
 walk_pmd_range mm/pagewalk.c:53 [inline]
 walk_pud_range mm/pagewalk.c:112 [inline]
 walk_p4d_range mm/pagewalk.c:139 [inline]
 walk_pgd_range mm/pagewalk.c:166 [inline]
 __walk_page_range+0x45a/0xc20 mm/pagewalk.c:261
 walk_page_range+0x179/0x310 mm/pagewalk.c:349
 madvise_pageout_page_range mm/madvise.c:506 [inline]
 madvise_pageout+0x1f0/0x330 mm/madvise.c:542
 madvise_vma mm/madvise.c:931 [inline]
 __do_sys_madvise+0x7d2/0x1600 mm/madvise.c:1113
 do_syscall_64+0x9f/0x4c0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

madvise_pageout access the specified range of the vma and isolate
them, then run shrink_page_list to reclaim the memory. But It also
isolate the unevictable page to reclaim. Hence, we can catch the
cases in shrink_page_list.

We can fix it by preventing unevictable page from isolating.
Another way to fix the issue by removing the condition of
BUG_ON(PageUnevictable(page)) in shrink_page_list. I think it
is better  to use the latter. Because We has taken the unevictable
page and skip it into account in shrink_page_list.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f7d1301..1c6e959 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1524,7 +1524,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		unlock_page(page);
 keep:
 		list_add(&page->lru, &ret_pages);
-		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
+		VM_BUG_ON_PAGE(PageLRU(page), page);
 	}
 
 	pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
-- 
1.7.12.4