[syzbot] [trace?] KCSAN: data-race in __rb_reserve_next / ring_buffer_iter_peek

[syzbot <syzbot+b57601b220ccc4fa1551@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    f9a2394a2348 Merge tag 'mm-hotfixes-stable-2026-08-06-18-4..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14ba2132580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=b57601b220ccc4fa1551
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/82bd4b0b2828/disk-f9a2394a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ab3cb0b1997d/vmlinux-f9a2394a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b0a8ddb2683a/bzImage-f9a2394a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b57601b220ccc4fa1551@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __rb_reserve_next / ring_buffer_iter_peek

write to 0xffff8881331f4000 of 8 bytes by task 12741 on cpu 0:
 __rb_reserve_next+0x5f1/0x6c0 kernel/trace/ring_buffer.c:4851
 rb_reserve_next_event kernel/trace/ring_buffer.c:4925 [inline]
 ring_buffer_lock_reserve+0x68c/0x830 kernel/trace/ring_buffer.c:4984
 __trace_buffer_lock_reserve kernel/trace/trace.h:1676 [inline]
 trace_event_buffer_lock_reserve+0x148/0x300 kernel/trace/trace.c:1924
 trace_event_buffer_reserve+0x120/0x180 kernel/trace/trace_events.c:688
 do_trace_event_raw_event_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 trace_event_raw_event_kmem_cache_free+0xa4/0x140 include/trace/events/kmem.h:117
 __do_trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 trace_kmem_cache_free include/trace/events/kmem.h:117 [inline]
 kmem_cache_free+0x31d/0x380 mm/slub.c:6503
 anon_vma_chain_free mm/rmap.c:147 [inline]
 unlink_anon_vmas+0x1b8/0x360 mm/rmap.c:514
 free_pgtables+0x50e/0x630 mm/memory.c:414
 exit_mmap+0x367/0x5e0 mm/mmap.c:1312
 __mmput+0x28/0x1c0 kernel/fork.c:1187
 mmput+0x40/0x50 kernel/fork.c:1210
 exec_mm_put_old fs/exec.c:916 [inline]
 setup_new_exec+0x20a/0x230 fs/exec.c:1353
 load_elf_binary+0x77a/0x1a30 fs/binfmt_elf.c:1024
 search_binary_handler fs/exec.c:1694 [inline]
 exec_binprm fs/exec.c:1726 [inline]
 bprm_execve+0x45c/0x9b0 fs/exec.c:1778
 do_execveat_common+0x7a4/0x8a0 fs/exec.c:1876
 __do_sys_execve fs/exec.c:1949 [inline]
 __se_sys_execve fs/exec.c:1943 [inline]
 __x64_sys_execve+0x5f/0x80 fs/exec.c:1943
 x64_sys_call+0x2752/0x3020 arch/x86/include/generated/asm/syscalls_64.h:60
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881331f4000 of 8 bytes by task 11658 on cpu 1:
 ring_buffer_iter_empty kernel/trace/ring_buffer.c:5647 [inline]
 rb_iter_peek kernel/trace/ring_buffer.c:6143 [inline]
 ring_buffer_iter_peek+0x265/0xb10 kernel/trace/ring_buffer.c:6305
 peek_next_entry kernel/trace/trace.c:2349 [inline]
 __find_next_entry+0x1a9/0x420 kernel/trace/trace.c:2398
 trace_find_next_entry_inc kernel/trace/trace.c:2672 [inline]
 s_next+0x10e/0x370 kernel/trace/trace.c:2711
 traverse+0x1c1/0x3b0 fs/seq_file.c:121
 seq_read_iter+0x7dc/0x8f0 fs/seq_file.c:196
 do_iter_readv_writev+0x4f6/0x5a0 fs/read_write.c:-1
 vfs_readv+0x1e8/0x6d0 fs/read_write.c:1019
 do_preadv fs/read_write.c:1133 [inline]
 __do_sys_preadv2 fs/read_write.c:1192 [inline]
 __se_sys_preadv2+0xfc/0x1c0 fs/read_write.c:1183
 __x64_sys_preadv2+0x67/0x80 fs/read_write.c:1183
 x64_sys_call+0x2b3b/0x3020 arch/x86/include/generated/asm/syscalls_64.h:328
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000001502ab37190 -> 0x000001505958442b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 11658 Comm: syz.6.11885 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================


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