==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff866685c8 of 8 bytes by task 7312 on cpu 1:
 data_alloc+0x291/0x2c0 kernel/printk/printk_ringbuffer.c:1096
 prb_reserve+0x85e/0xb60 kernel/printk/printk_ringbuffer.c:1669
 vprintk_store+0x558/0x870 kernel/printk/printk.c:2326
 vprintk_emit+0x168/0x690 kernel/printk/printk.c:2408
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2447
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7a/0xa0 kernel/printk/printk.c:2457
 show_ip arch/x86/kernel/dumpstack.c:142 [inline]
 show_iret_regs+0x27/0x60 arch/x86/kernel/dumpstack.c:149
 __show_regs+0x2b/0x450 arch/x86/kernel/process_64.c:76
 show_trace_log_lvl+0x348/0x400 arch/x86/kernel/dumpstack.c:301
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xf2/0x150 lib/dump_stack.c:120
 dump_stack+0x15/0x1a lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x24a/0x260 lib/fault-inject.c:174
 should_failslab+0x8f/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4068 [inline]
 slab_alloc_node mm/slub.c:4144 [inline]
 __do_kmalloc_node mm/slub.c:4293 [inline]
 __kmalloc_noprof+0xab/0x3f0 mm/slub.c:4306
 kmalloc_noprof include/linux/slab.h:905 [inline]
 kzalloc_noprof include/linux/slab.h:1037 [inline]
 kobject_get_path+0x8f/0x1c0 lib/kobject.c:161
 kobject_uevent_env+0x1b9/0x550 lib/kobject_uevent.c:545
 kobject_uevent+0x1c/0x30 lib/kobject_uevent.c:656
 device_del+0x6fa/0x780 drivers/base/core.c:3873
 device_unregister+0x15/0x40 drivers/base/core.c:3896
 bdi_unregister+0x307/0x3a0 mm/backing-dev.c:1170
 del_gendisk+0x2f4/0x5f0 block/genhd.c:718
 loop_remove drivers/block/loop.c:2124 [inline]
 loop_control_remove drivers/block/loop.c:2183 [inline]
 loop_control_ioctl+0x3ae/0x440 drivers/block/loop.c:2221
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x1690/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff866685c8 of 8 bytes by task 7313 on cpu 0:
 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+0x235/0xb60 kernel/printk/printk_ringbuffer.c:1619
 vprintk_store+0x558/0x870 kernel/printk/printk.c:2326
 vprintk_emit+0x168/0x690 kernel/printk/printk.c:2408
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2447
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x7a/0xa0 kernel/printk/printk.c:2457
 sg_write+0x6ec/0x710 drivers/scsi/sg.c:694
 do_loop_readv_writev fs/read_write.c:843 [inline]
 vfs_writev+0x3fa/0x880 fs/read_write.c:1052
 do_writev+0xf4/0x220 fs/read_write.c:1096
 __do_sys_writev fs/read_write.c:1164 [inline]
 __se_sys_writev fs/read_write.c:1161 [inline]
 __x64_sys_writev+0x45/0x50 fs/read_write.c:1161
 x64_sys_call+0x1fab/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:21
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000016f838 -> 0x000000000023af88

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7313 Comm: syz.7.19570 Not tainted 6.14.0-rc6-syzkaller-00205-g3571e8b091f4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================
sg_write: data in/out 768/1 bytes for SCSI command 0x0-- guessing data in;
   program syz.7.19570 not setting count and/or reply_len properly