syzkaller0: entered allmulticast mode
==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff86869070 of 8 bytes by task 11446 on cpu 0:
 data_alloc+0x27d/0x2b0 kernel/printk/printk_ringbuffer.c:1096
 prb_reserve+0x808/0xaf0 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 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
 set_capacity_and_notify+0x14c/0x1f0 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:220
 loop_configure+0x825/0x9c0 drivers/block/loop.c:1077
 lo_ioctl+0x1e1/0x12b0 drivers/block/loop.c:1532
 blkdev_ioctl+0x34f/0x440 block/ioctl.c:705
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:584
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:584
 x64_sys_call+0x1816/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86869070 of 8 bytes by task 11444 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:482 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:778 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:924 [inline]
 prb_reserve+0x221/0xaf0 kernel/printk/printk_ringbuffer.c:1619
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 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
 __netdev_printk+0x321/0x3e0 net/core/dev.c:12606
 netdev_info+0x9b/0xd0 net/core/dev.c:12653
 __dev_set_promiscuity+0x233/0x450 net/core/dev.c:9361
 netif_set_promiscuity+0x39/0x90 net/core/dev.c:9396
 dev_set_promiscuity+0xc1/0x170 net/core/dev_api.c:287
 packet_dev_mc net/packet/af_packet.c:3697 [inline]
 packet_mc_add+0x3bb/0x570 net/packet/af_packet.c:3774
 packet_setsockopt+0xa3e/0xfd0 net/packet/af_packet.c:3859
 do_sock_setsockopt net/socket.c:2344 [inline]
 __sys_setsockopt+0x181/0x200 net/socket.c:2369
 __do_sys_setsockopt net/socket.c:2375 [inline]
 __se_sys_setsockopt net/socket.c:2372 [inline]
 __x64_sys_setsockopt+0x64/0x80 net/socket.c:2372
 x64_sys_call+0x20ec/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:55
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xfffffffffffc3e48 -> 0x000000000005a320

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 11444 Comm: syz.1.2856 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
syzkaller0: entered promiscuous mode
syzkaller0: left promiscuous mode
syzkaller0: left allmulticast mode