Re: (resend)WARNING: trying to isolate tail page in isolate_lru_page

[Minchan Kim <minchan@kernel.org>]

On Fri, Aug 26, 2022 at 11:20:58AM +0800, Yin, Fengwei wrote:
> 
> 
> On 8/26/2022 2:46 AM, Matthew Wilcox wrote:
> >>> Looks like my analysis from yesterday was dropped:
> >>>
> >>> : This all seems quite plausible.  The reproducer seems to (correct me
> >>> : if I'm wrong) create an AF_PACKET socket and mmap it.  af_packet.c
> >>> : seems to create compound pages and mmap them.  This isn't folio-related
> >>> : at all; I just moved the code that warns about it from mm/vmscan.c to
> >>> : folio-compat.c.
> >>> :
> >>> : Looks like a long-standing bug in MADV_PAGEOUT to me.
> >> Such page should never be on lru, right? We could test lru before
> >> calling isolate_lru_page() for this case? I know isolate_lru_page()
> >> does the check, but the tail page warning is raised before the check.
> >>
> >> Could the tail page warning be moved under the lru flag test? Seems
> >> possible, but it should need extra handling (re-set lru flag). Seems a
> >> little bit overkilling.
> > There's a number of ways of solving this.  I'm interested in seeing
> > which one Minchan thinks is best.
> > 
> 
> My understanding is:
> PageTransCompound() return false for compound page if THP is disabled
> in kernel config. Replacing PageTransCompound() with PageCompound() 
> could work here. But for the long term, folio should be the answer. :).

Thanks for reporting and analysis, folks,

I agree with Yang since the MADV_PAGEOUT should work with only
LRU pages.

From 0a43ac31c903bc23299a868a6d6724ff5b807e3d Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 26 Aug 2022 09:37:34 -0700
Subject: [PATCH] mm: fix madivse_pageout mishandling on non-LRU page
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

MADV_PAGEOUT tries to isolate non-LRU pages and get the warning
from isolate_lru_page below.
Fix it with checking PageLRU in advance.

------------[ cut here ]------------
trying to isolate tail page
WARNING: CPU: 0 PID: 6175 at mm/folio-compat.c:158 isolate_lru_page+0x130/0x140
Modules linked in:
CPU: 0 PID: 6175 Comm: syz-executor.0 Not tainted 5.18.12 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:isolate_lru_page+0x130/0x140

Link: https://lore.kernel.org/linux-mm/485f8c33.2471b.182d5726afb.Coremail.hantianshuo@iie.ac.cn/
Reported-by: 韩天硕 <hantianshuo@iie.ac.cn>
Suggested-by: Yang Shi <shy828301@gmail.com>
Fixes: 1a4e58cce84e ("mm: introduce MADV_PAGEOUT")
Cc: stable@vger.kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/madvise.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 682e1d161aef..a3fc4cd32ed3 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -452,8 +452,11 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 			continue;
 		}
 
-		/* Do not interfere with other mappings of this page */
-		if (page_mapcount(page) != 1)
+		/*
+		 * Do not interfere with other mappings of this page and
+		 * non-LRU page.
+		 */
+		if (!PageLRU(page) || page_mapcount(page) != 1)
 			continue;
 
 		VM_BUG_ON_PAGE(PageTransCompound(page), page);
-- 
2.37.2.672.g94769d06f0-goog