[moderation] [mm?] KCSAN: data-race in _prb_read_valid / prb_reserve_in_last

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 405e6c37c89e Merge tag 'probes-fixes-v6.15-rc6' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1673ecd4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=340628a183bd72b7
dashboard link: https://syzkaller.appspot.com/bug?extid=e5150f7a4fcbf3fffca0
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linu...@kvack.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d20eee28550b/disk-405e6c37.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/26388aec580f/vmlinux-405e6c37.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ea00d483db23/bzImage-405e6c37.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e5150f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _prb_read_valid / prb_reserve_in_last

write to 0xffffffff86877d10 of 8 bytes by task 4561 on cpu 0:
data_realloc kernel/printk/printk_ringbuffer.c:1177 [inline]
prb_reserve_in_last+0x861/0xb80 kernel/printk/printk_ringbuffer.c:1440
vprintk_store+0x494/0x860 kernel/printk/printk.c:2300
vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
_printk+0x79/0xa0 kernel/printk/printk.c:2475
show_free_areas mm/show_mem.c:382 [inline]
__show_mem+0x1132/0x14e0 mm/show_mem.c:407
warn_alloc_show_mem mm/page_alloc.c:3738 [inline]
warn_alloc+0x189/0x1a0 mm/page_alloc.c:3763
__vmalloc_node_range_noprof+0x28e/0xdf0 mm/vmalloc.c:3810
__vmalloc_node_noprof mm/vmalloc.c:3908 [inline]
__vmalloc_noprof+0x5f/0x70 mm/vmalloc.c:3922
bpf_prog_alloc_no_stats+0x47/0x390 kernel/bpf/core.c:104
bpf_prog_alloc+0x3c/0x150 kernel/bpf/core.c:146
bpf_prog_load+0x514/0x1070 kernel/bpf/syscall.c:2881
__sys_bpf+0x51d/0x790 kernel/bpf/syscall.c:5834
__do_sys_bpf kernel/bpf/syscall.c:5941 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5939 [inline]
__x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:5939
x64_sys_call+0x2478/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86877d08 of 16 bytes by task 2996 on cpu 1:
desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1874 [inline]
prb_read kernel/printk/printk_ringbuffer.c:1922 [inline]
_prb_read_valid+0x1bc/0x920 kernel/printk/printk_ringbuffer.c:2113
prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2185
syslog_print+0x146/0x540 kernel/printk/printk.c:1633
do_syslog+0x52b/0x7e0 kernel/printk/printk.c:1785
__do_sys_syslog kernel/printk/printk.c:1877 [inline]
__se_sys_syslog kernel/printk/printk.c:1875 [inline]
__x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1875
x64_sys_call+0x2ea0/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:104
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2996 Comm: klogd Not tainted 6.15.0-rc6-syzkaller-00051-g405e6c37c89e #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.