Forwarded: Re: [Internet][syzbot ci] Re: memcg: fix dying memcg pinned by swapped out shmem pages

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Subject: Re: [Internet][syzbot ci] Re: memcg: fix dying memcg pinned by swapped out shmem pages
Author: bingfangguo@tencent.com

#syz test



                    syzbot ci<syzbot+ci49bb3ed471ef5f9f@syzkaller.appspotmail.com&gt;&nbsp;在 2026年8月13日 周四 21:26 写道：

syzbot ci has tested the following series

[v1] memcg: fix dying memcg pinned by swapped out shmem pages
https://lore.kernel.org/all/20260813-memcgid-objcg-v1-0-83d21c685b77@tencent.com
* [PATCH RFC 1/5] memcg: move memcg private ID refcount to objcg
* [PATCH RFC 2/5] memcg: get stable memcg first before getting memcgid reference
* [PATCH RFC 3/5] memcg: remove retry logic in mem_cgroup_private_id_get_online
* [PATCH RFC 4/5] memcg: add a helper to get online memcg from memcgid
* [PATCH RFC 5/5] memcg: filter out reparented memcgs got using memcgid

and found the following issue:
WARNING: refcount bug in __mem_cgroup_uncharge_swap

Full report is available here:
https://ci.syzbot.org/series/3a8a2a5f-8b6d-4abf-954e-a1a18ee62748

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WARNING: refcount bug in __mem_cgroup_uncharge_swap

tree:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; linux-next
URL:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next
base:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 288058d8db5d35623228d84f48d9bea3707d5c85
arch:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; amd64
compiler:&nbsp; Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:&nbsp;&nbsp;&nbsp; https://ci.syzbot.org/builds/35dac6f6-b44a-4ea8-9adf-2cdda5584e45/config
syz repro: https://ci.syzbot.org/findings/6e117c0b-d6e2-44a6-8e35-161cb33f2aff/syz_repro

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: syz.2.19/5863
Modules linked in:
CPU: 0 UID: 0 PID: 5863 Comm: syz.2.19 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:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: 64 84 8e 0b 67 48 0f b9 3a eb 4a e8 58 fa f2 fc 48 8d 3d 61 84 8e 0b 67 48 0f b9 3a eb 37 e8 45 fa f2 fc 48 8d 3d 5e 84 8e 0b <67&gt; 48 0f b9 3a eb 24 e8 32 fa f2 fc 48 8d 3d 5b 84 8e 0b 67 48 0f
RSP: 0018:ffffc90003bbf1d0 EFLAGS: 00010293
RAX: ffffffff84d3ed9b RBX: 0000000000000003 RCX: ffff8881bdf58000
RDX: 0000000000000000 RSI: ffffffff8f363380 RDI: ffffffff90627200
RBP: 1ffffffff20ae968 R08: ffff8881bdf58000 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: ffff8881026f8000
R13: ffff88810a914100 R14: ffff88810a914134 R15: 1ffff110204df009
FS:&nbsp; 00007fe2ee63d6c0(0000) GS:ffff88818d960000(0000) knlGS:0000000000000000
CS:&nbsp; 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056066247f0b8 CR3: 000000000e946000 CR4: 00000000000006f0
Call Trace:
&nbsp;<TASK&gt;
&nbsp;mem_cgroup_take_from_private_id mm/memcontrol.c:4049 [inline]
&nbsp;__mem_cgroup_uncharge_swap+0x204/0x2a0 mm/memcontrol.c:5707
&nbsp;mem_cgroup_uncharge_swap include/linux/swap.h:520 [inline]
&nbsp;__swap_cluster_free_entries+0x735/0xc50 mm/swapfile.c:1955
&nbsp;swap_put_entries_cluster+0x3b1/0x4b0 mm/swapfile.c:1629
&nbsp;swap_put_entries_direct+0x137/0x210 mm/swapfile.c:2139
&nbsp;zap_nonpresent_ptes mm/memory.c:1838 [inline]
&nbsp;do_zap_pte_range mm/memory.c:1905 [inline]
&nbsp;zap_pte_range mm/memory.c:2003 [inline]
&nbsp;zap_pmd_range mm/memory.c:2089 [inline]
&nbsp;zap_pud_range mm/memory.c:2117 [inline]
&nbsp;zap_p4d_range mm/memory.c:2138 [inline]
&nbsp;__zap_vma_range+0x1d9d/0x4f10 mm/memory.c:2178
&nbsp;unmap_vmas+0x390/0x550 mm/memory.c:2247
&nbsp;exit_mmap+0x293/0x9f0 mm/mmap.c:1315
&nbsp;__mmput+0x118/0x420 kernel/fork.c:1187
&nbsp;exit_mm+0x221/0x2d0 kernel/exit.c:615
&nbsp;do_exit+0x6cd/0x2360 kernel/exit.c:997
&nbsp;do_group_exit+0x22d/0x2f0 kernel/exit.c:1152
&nbsp;get_signal+0x121b/0x12c0 kernel/signal.c:3046
&nbsp;arch_do_signal_or_restart+0xbb/0x860 arch/x86/kernel/signal.c:337
&nbsp;__exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
&nbsp;exit_to_user_mode_loop+0x104/0x730 kernel/entry/common.c:101
&nbsp;__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
&nbsp;syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
&nbsp;syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
&nbsp;do_syscall_64+0x353/0x580 arch/x86/entry/syscall_64.c:100
&nbsp;entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe2ed79e0d9
Code: Unable to access opcode bytes at 0x7fe2ed79e0af.
RSP: 002b:00007fe2ee63d0e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fe2eda25fa8 RCX: 00007fe2ed79e0d9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fe2eda25fa8
RBP: 00007fe2eda25fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe2eda26038 R14: 00007fff0bed41b0 R15: 00007fff0bed4298
&nbsp;</TASK&gt;
----------------
Code disassembly (best guess):
&nbsp;&nbsp; 0:	64 84 8e 0b 67 48 0f 	test&nbsp;&nbsp; %cl,%fs:0xf48670b(%rsi)
&nbsp;&nbsp; 7:	b9 3a eb 4a e8&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	mov&nbsp;&nbsp;&nbsp; $0xe84aeb3a,%ecx
&nbsp;&nbsp; c:	58&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	pop&nbsp;&nbsp;&nbsp; %rax
&nbsp;&nbsp; d:	fa&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	cli
&nbsp;&nbsp; e:	f2 fc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	repnz cld
&nbsp; 10:	48 8d 3d 61 84 8e 0b 	lea&nbsp;&nbsp;&nbsp; 0xb8e8461(%rip),%rdi&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # 0xb8e8478
&nbsp; 17:	67 48 0f b9 3a&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	ud1&nbsp;&nbsp;&nbsp; (%edx),%rdi
&nbsp; 1c:	eb 37&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	jmp&nbsp;&nbsp;&nbsp; 0x55
&nbsp; 1e:	e8 45 fa f2 fc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	call&nbsp;&nbsp; 0xfcf2fa68
&nbsp; 23:	48 8d 3d 5e 84 8e 0b 	lea&nbsp;&nbsp;&nbsp; 0xb8e845e(%rip),%rdi&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # 0xb8e8488
* 2a:	67 48 0f b9 3a&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	ud1&nbsp;&nbsp;&nbsp; (%edx),%rdi <-- trapping instruction
&nbsp; 2f:	eb 24&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	jmp&nbsp;&nbsp;&nbsp; 0x55
&nbsp; 31:	e8 32 fa f2 fc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	call&nbsp;&nbsp; 0xfcf2fa68
&nbsp; 36:	48 8d 3d 5b 84 8e 0b 	lea&nbsp;&nbsp;&nbsp; 0xb8e845b(%rip),%rdi&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # 0xb8e8498
&nbsp; 3d:	67&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	addr32
&nbsp; 3e:	48&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	rex.W
&nbsp; 3f:	0f&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 	.byte 0xf


***

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

---
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