linux-kernel - Re: [syzbot] [mm?] WARNING in unmap_page

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Date:   Wed, 15 Nov 2023 14:00:06 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com>
Cc:     david@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, usama.anjum@...labora.com,
        wangkefeng.wang@...wei.com
Subject: Re: [syzbot] [mm?] WARNING in unmap_page_range (2)

On Wed, 15 Nov 2023 05:32:19 -0800 syzbot <syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ac347a0655db Merge tag 'arm64-fixes' of git://git.kernel.o..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15ff3057680000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=287570229f5c0a7c
> dashboard link: https://syzkaller.appspot.com/bug?extid=7ca4b2719dc742b8d0a4
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=162a25ff680000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13d62338e80000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/00e30e1a5133/disk-ac347a06.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/07c43bc37935/vmlinux-ac347a06.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/c6690c715398/bzImage-ac347a06.xz
> 
> The issue was bisected to:
> 
> commit 12f6b01a0bcbeeab8cc9305673314adb3adf80f7
> Author: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Date:   Mon Aug 21 14:15:15 2023 +0000
> 
>     fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag

Thanks.  The bisection is surprising, but the mentioned patch does
mess with pagemap.

How about we add this?

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm/memory.c:zap_pte_range() print bad swap entry
Date: Wed Nov 15 01:54:18 PM PST 2023

We have a report of this WARN() triggering.  Let's print the offending
swp_entry_t to help diagnosis.

Link: https://lkml.kernel.org/r/000000000000b0e576060a30ee3b@google.com
Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/memory.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/memory.c~a
+++ a/mm/memory.c
@@ -1521,6 +1521,7 @@ static unsigned long zap_pte_range(struc
 				continue;
 		} else {
 			/* We should have covered all the swap entry types */
+			pr_alert("unrecognized swap entry 0x%lx\n", entry.val);
 			WARN_ON_ONCE(1);
 		}
 		pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
_