[syzbot] [cgroups?] [mm?] KASAN: wild-memory-access Read in lookup_swap_cgroup_id (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 18f7fcd5e69a Linux 6.19-rc8
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1428fc5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=e12bd9ca48157add237a
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2c19d9acc149/disk-18f7fcd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/02cf07c94e58/vmlinux-18f7fcd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/84011cec9819/bzImage-18f7fcd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e12bd9...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: wild-memory-access in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: wild-memory-access in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: wild-memory-access in __swap_cgroup_id_lookup mm/swap_cgroup.c:28 [inline]
BUG: KASAN: wild-memory-access in lookup_swap_cgroup_id+0xf9/0x1a0 mm/swap_cgroup.c:127
Read of size 4 at addr 0007fffffffffffc by task syz.5.3598/20029

CPU: 1 UID: 0 PID: 20029 Comm: syz.5.3598 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
kasan_report+0xdf/0x1a0 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:186 [inline]
kasan_check_range+0x10f/0x1e0 mm/kasan/generic.c:200
instrument_atomic_read include/linux/instrumented.h:68 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
__swap_cgroup_id_lookup mm/swap_cgroup.c:28 [inline]
lookup_swap_cgroup_id+0xf9/0x1a0 mm/swap_cgroup.c:127
swap_pte_batch+0x3c3/0x720 mm/internal.h:390
zap_nonpresent_ptes mm/memory.c:1749 [inline]
do_zap_pte_range mm/memory.c:1818 [inline]
zap_pte_range mm/memory.c:1858 [inline]
zap_pmd_range mm/memory.c:1950 [inline]
zap_pud_range mm/memory.c:1978 [inline]
zap_p4d_range mm/memory.c:1999 [inline]
unmap_page_range+0x1f6f/0x43e0 mm/memory.c:2020
unmap_single_vma+0x153/0x240 mm/memory.c:2062
unmap_vmas+0x218/0x470 mm/memory.c:2104
exit_mmap+0x181/0xae0 mm/mmap.c:1277
__mmput+0x12a/0x410 kernel/fork.c:1173
mmput+0x67/0x80 kernel/fork.c:1196
exit_mm kernel/exit.c:581 [inline]
do_exit+0x78a/0x2a30 kernel/exit.c:959
do_group_exit+0xd5/0x2a0 kernel/exit.c:1112
get_signal+0x1ec7/0x21e0 kernel/signal.c:3034
arch_do_signal_or_restart+0x91/0x7a0 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
exit_to_user_mode_loop+0x86/0x4b0 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x4fe/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2f8f19aeb9
Code: Unable to access opcode bytes at 0x7f2f8f19ae8f.
RSP: 002b:00007f2f900350e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f2f8f416098 RCX: 00007f2f8f19aeb9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f2f8f416098
RBP: 00007f2f8f416090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2f8f416128 R14: 00007ffc0c8cc050 R15: 00007ffc0c8cc138
</TASK>
==================================================================


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[Dmitry Vyukov]

This happened before:
https://lore.kernel.org/all/67d04360.050a022...@google.com/T/
and now 2 more times.
All reports look similar: exit_mm -> zap_p4d_range
And all access addresses look the same: top 13 bits are zeros, then
some garbage (0007fffffffffffc).
I am pretty sure it's telling us something, some kind of tricky race,
rather than a previous corruption. Swp entry is somehow invalid?

[Shakeel Butt]

+Kairui

Thanks for the report. It would be good to have a reproducer. I will dig
deeper later but good to have eyes from Kairui who has recent changes
in the area.