[syzbot ci] Re: mm, swap: swap table phase III: remove swap_map

[syzbot ci] Re: mm, swap: swap table phase III: remove swap_map

[syzbot ci]

syzbot ci has tested the following series

[v1] mm, swap: swap table phase III: remove swap_map
https://lore.kernel.org/all/20260126-swap-table-p3-v1-0-a74155fab9b0@tencent.com
* [PATCH 01/12] mm, swap: protect si->swap_file properly and use as a mount indicator
* [PATCH 02/12] mm, swap: clean up swapon process and locking
* [PATCH 03/12] mm, swap: remove redundant arguments and locking for enabling a device
* [PATCH 04/12] mm, swap: consolidate bad slots setup and make it more robust
* [PATCH 05/12] mm/workingset: leave highest bits empty for anon shadow
* [PATCH 06/12] mm, swap: implement helpers for reserving data in the swap table
* [PATCH 07/12] mm, swap: mark bad slots in swap table directly
* [PATCH 08/12] mm, swap: simplify swap table sanity range check
* [PATCH 09/12] mm, swap: use the swap table to track the swap count
* [PATCH 10/12] mm, swap: no need to truncate the scan border
* [PATCH 11/12] mm, swap: simplify checking if a folio is swapped
* [PATCH 12/12] mm, swap: no need to clear the shadow explicitly

and found the following issue:
WARNING in swap_cluster_lock

Full report is available here:
https://ci.syzbot.org/series/3f6169fc-e24a-4a19-ba56-e5907b448edc

***

WARNING in swap_cluster_lock

tree:      mm-new
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base:      5a3704ed2dce0b54a7f038b765bb752b87ee8cc2
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/0eabd97a-86d8-4606-9d94-dbe4e7fd7c07/config
C repro:   https://ci.syzbot.org/findings/5b039fd0-70da-4954-817d-8bf86315c684/c_repro
syz repro: https://ci.syzbot.org/findings/5b039fd0-70da-4954-817d-8bf86315c684/syz_repro

------------[ cut here ]------------
offset >= si->max
WARNING: mm/swap.h:88 at __swap_offset_to_cluster mm/swap.h:88 [inline], CPU#1: syz.0.548/6508
WARNING: mm/swap.h:88 at __swap_cluster_lock mm/swap.h:101 [inline], CPU#1: syz.0.548/6508
WARNING: mm/swap.h:88 at swap_cluster_lock+0xef/0x130 mm/swap.h:132, CPU#1: syz.0.548/6508
Modules linked in:
CPU: 1 UID: 0 PID: 6508 Comm: syz.0.548 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:__swap_offset_to_cluster mm/swap.h:88 [inline]
RIP: 0010:__swap_cluster_lock mm/swap.h:101 [inline]
RIP: 0010:swap_cluster_lock+0xef/0x130 mm/swap.h:132
Code: e8 86 3b 5a 09 4c 89 f8 5b 41 5c 41 5e 41 5f 5d e9 86 86 5a 09 cc e8 90 ff a0 ff 90 0f 0b 90 e9 3f ff ff ff e8 82 ff a0 ff 90 <0f> 0b 90 e9 6f ff ff ff e8 74 ff a0 ff 90 0f 0b 90 eb a4 e8 69 ff
RSP: 0018:ffffc90004ae66c0 EFLAGS: 00010293
RAX: ffffffff82219a6e RBX: 0000000000007a12 RCX: ffff888110363a80
RDX: 0000000000000000 RSI: 0000000000007a12 RDI: 0000000000007a12
RBP: 0000000000007a12 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff5200095cccc R12: dffffc0000000000
R13: ffff888175c2a010 R14: ffff888175c2a000 R15: 0000000000007a12
FS:  000055556978b500(0000) GS:ffff8882a9923000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fca0a017dac CR3: 0000000112e64000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 cluster_alloc_swap_entry+0x20f/0xa40 mm/swapfile.c:1090
 swap_alloc_slow mm/swapfile.c:1385 [inline]
 folio_alloc_swap+0x81f/0x1190 mm/swapfile.c:1717
 shrink_folio_list+0x2714/0x52b0 mm/vmscan.c:1306
 reclaim_folio_list+0x100/0x4f0 mm/vmscan.c:2205
 reclaim_pages+0x45b/0x530 mm/vmscan.c:2242
 madvise_cold_or_pageout_pte_range+0x19b9/0x1d00 mm/madvise.c:561
 walk_pmd_range mm/pagewalk.c:130 [inline]
 walk_pud_range mm/pagewalk.c:224 [inline]
 walk_p4d_range mm/pagewalk.c:262 [inline]
 walk_pgd_range+0x1032/0x1d30 mm/pagewalk.c:303
 __walk_page_range+0x14c/0x710 mm/pagewalk.c:411
 walk_page_range_vma_unsafe+0x309/0x410 mm/pagewalk.c:715
 madvise_pageout_page_range mm/madvise.c:620 [inline]
 madvise_pageout mm/madvise.c:645 [inline]
 madvise_vma_behavior+0x382e/0x4240 mm/madvise.c:1364
 madvise_walk_vmas+0x573/0xae0 mm/madvise.c:1719
 madvise_do_behavior+0x386/0x540 mm/madvise.c:1935
 do_madvise+0x1fa/0x2e0 mm/madvise.c:2028
 __do_sys_madvise mm/madvise.c:2037 [inline]
 __se_sys_madvise mm/madvise.c:2035 [inline]
 __x64_sys_madvise+0xa6/0xc0 mm/madvise.c:2035
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fca09d9acb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe78abed08 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007fca0a015fa0 RCX: 00007fca09d9acb9
RDX: 0000000000000015 RSI: 0000000000600003 RDI: 0000200000000000
RBP: 00007fca09e08bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fca0a015fac R14: 00007fca0a015fa0 R15: 00007fca0a015fa0
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

Re: [syzbot ci] Re: mm, swap: swap table phase III: remove swap_map

[Kairui Song]

On Sun, Jan 25, 2026 at 02:13:41PM +0800, syzbot ci wrote:
> syzbot ci has tested the following series
> 
> [v1] mm, swap: swap table phase III: remove swap_map
> https://lore.kernel.org/all/20260126-swap-table-p3-v1-0-a74155fab9b0@tencent.com
> * [PATCH 01/12] mm, swap: protect si->swap_file properly and use as a mount indicator
> * [PATCH 02/12] mm, swap: clean up swapon process and locking
> * [PATCH 03/12] mm, swap: remove redundant arguments and locking for enabling a device
> * [PATCH 04/12] mm, swap: consolidate bad slots setup and make it more robust
> * [PATCH 05/12] mm/workingset: leave highest bits empty for anon shadow
> * [PATCH 06/12] mm, swap: implement helpers for reserving data in the swap table
> * [PATCH 07/12] mm, swap: mark bad slots in swap table directly
> * [PATCH 08/12] mm, swap: simplify swap table sanity range check
> * [PATCH 09/12] mm, swap: use the swap table to track the swap count
> * [PATCH 10/12] mm, swap: no need to truncate the scan border
> * [PATCH 11/12] mm, swap: simplify checking if a folio is swapped
> * [PATCH 12/12] mm, swap: no need to clear the shadow explicitly
> 
> and found the following issue:
> WARNING in swap_cluster_lock
> 
> Full report is available here:
> https://ci.syzbot.org/series/3f6169fc-e24a-4a19-ba56-e5907b448edc
> 
> ***
> 
> WARNING in swap_cluster_lock
> 
> tree:      mm-new
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
> base:      5a3704ed2dce0b54a7f038b765bb752b87ee8cc2
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/0eabd97a-86d8-4606-9d94-dbe4e7fd7c07/config
> C repro:   https://ci.syzbot.org/findings/5b039fd0-70da-4954-817d-8bf86315c684/c_repro
> syz repro: https://ci.syzbot.org/findings/5b039fd0-70da-4954-817d-8bf86315c684/syz_repro
> 
> ------------[ cut here ]------------
> offset >= si->max
> WARNING: mm/swap.h:88 at __swap_offset_to_cluster mm/swap.h:88 [inline], CPU#1: syz.0.548/6508
> WARNING: mm/swap.h:88 at __swap_cluster_lock mm/swap.h:101 [inline], CPU#1: syz.0.548/6508
> WARNING: mm/swap.h:88 at swap_cluster_lock+0xef/0x130 mm/swap.h:132, CPU#1: syz.0.548/6508

This is a good catch from the bot. It's caused by the patch "[PATCH 10/12] mm, swap: no need to truncate the scan border", however that patch is not wrong, it just have to update the debug check too:

diff --git a/mm/swap.h b/mm/swap.h
index 087cef49cf69..386a289ef8e7 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -85,7 +85,7 @@ static inline struct swap_cluster_info *__swap_offset_to_cluster(
                struct swap_info_struct *si, pgoff_t offset)
 {
        VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
-       VM_WARN_ON_ONCE(offset >= si->max);
+       VM_WARN_ON_ONCE(offset >= roundup(si->max, SWAPFILE_CLUSTER));
        return &si->cluster_info[offset / SWAPFILE_CLUSTER];
 }

I'll update this in V2.