[RFC PATCH stable 5.10/5.15] mm: Pass head page to clear_page_mlock for page_remove_rmap

[Wupeng Ma]

From: Ma Wupeng <mawupeng1@xxxxxxxxxx>

Our syzbot report a mlock related problem. During exit_mm, tail page is
passed to clear_page_mlock which final lead to kernel panic.

During unmap_page_range, if compound is false, it means this page is
seen as a small page. This page is passed to isolate_lru_page if this
page is PageMlocked and finally lead to "trying to isolate tail page"
warning.

Here is the simplified calltrace:

unmap_page_range
  zap_pte_range
    page_remove_rmap(page, false);	// compound is false means to handle
					   to small page not compound page
	  nr_pages = thp_nr_pages(page);
	  clear_page_mlock(page)	// maybe tail page here
		isolate_lru_page
		  WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");

Since mlock is not supposed to handle tail, we pass head page to
clear_page_mlock() to slove this problem.

This bug can lead to multiple reports. Here ares the simplified reports:

------------[ cut here ]------------
trying to isolate tail page
WARNING: CPU: 1 PID: 24489 at mm/vmscan.c:2031 isolate_lru_page+0x574/0x660

page:fffffc000eb7a300 refcount:512 mapcount:0 mapping:0000000000000000 index:0x2008c pfn:0x3ede8c
head:fffffc000eb78000 order:9 compound_mapcount:0 compound_pincount:0
memcg:ffff0000d24bc000
anon flags: 0x37ffff80009080c(uptodate|dirty|arch_1|head|swapbacked|node=1|zone=2|lastcpupid=0xfffff)
raw: 037ffff800000800 fffffc000eb78001 fffffc000eb7a308 dead000000000400
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
head: 037ffff80009080c fffffc000eb70008 fffffc000e350708 ffff0003829eb839
head: 0000000000020000 0000000000000000 00000200ffffffff ffff0000d24bc000
page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg && !mem_cgroup_disabled())
------------[ cut here ]------------
WARNING: CPU: 1 PID: 24489 at include/linux/memcontrol.h:767 lock_page_lruvec_irq+0x148/0x190

page:fffffc000eb7a300 refcount:0 mapcount:0 mapping:dead000000000400 index:0x0 pfn:0x3ede8c
failed to read mapping contents, not a valid kernel address?
flags: 0x37ffff800000800(arch_1|node=1|zone=2|lastcpupid=0xfffff)
raw: 037ffff800000800 dead000000000100 dead000000000122 dead000000000400
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))
------------[ cut here ]------------
kernel BUG at include/linux/mm.h:1213!
Call trace:
 lru_cache_add+0x2d4/0x2e8
 putback_lru_page+0x2c/0x168
 clear_page_mlock+0x254/0x318
 page_remove_rmap+0x900/0x9c0
 unmap_page_range+0xa78/0x16a0
 unmap_single_vma+0x114/0x1a0
 unmap_vmas+0x100/0x220
 exit_mmap+0x120/0x410
 mmput+0x174/0x498
 exit_mm+0x33c/0x460
 do_exit+0x3c0/0x1310
 do_group_exit+0x98/0x170
 get_signal+0x370/0x13d0
 do_notify_resume+0x5a0/0x968
 el0_da+0x154/0x188
 el0t_64_sync_handler+0x88/0xb8
 el0t_64_sync+0x1a0/0x1a4
Code: 912b0021 aa1503e0 910c0021 9401a49c (d4210000)

This bug can be reproduced in both linux-5.10.y & linux-5.15.y and maybe
fixed after commit 889a3747b3b7 ("mm/lru: Add folio LRU functions").
This patch turn page into folio for LRU related operations, all
operations to page is turn to folio which means head page after this
patch.

Fixes: d281ee614518 ("rmap: add argument to charge compound page")
Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
---
 mm/rmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 330b361a460e..8838f6a9d65d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1372,7 +1372,7 @@ void page_remove_rmap(struct page *page, bool compound)
 	__dec_lruvec_page_state(page, NR_ANON_MAPPED);
 
 	if (unlikely(PageMlocked(page)))
-		clear_page_mlock(page);
+		clear_page_mlock(compound_head(page));
 
 	if (PageTransCompound(page))
 		deferred_split_huge_page(compound_head(page));
-- 
2.25.1