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

write to 0xffffffff8688c7b0 of 8 bytes by task 23828 on cpu 1:
 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
 _fat_msg+0xa4/0xd0 fs/fat/misc.c:62
 __fat_fs_error+0x178/0x1d0 fs/fat/misc.c:31
 fat_ent_read+0x52b/0x5a0 fs/fat/fatent.c:359
 fat_get_cluster+0x4b2/0x7b0 fs/fat/cache.c:266
 fat_bmap_cluster fs/fat/cache.c:299 [inline]
 fat_get_mapped_cluster+0xe4/0x240 fs/fat/cache.c:320
 fat_bmap+0x254/0x280 fs/fat/cache.c:384
 __fat_get_block fs/fat/inode.c:128 [inline]
 fat_get_block+0xd3/0x5e0 fs/fat/inode.c:189
 block_read_full_folio+0x1fa/0x6a0 fs/buffer.c:2427
 do_mpage_readpage+0xcf4/0xe20 fs/mpage.c:314
 mpage_readahead+0x1b7/0x2e0 fs/mpage.c:371
 fat_readahead+0x1c/0x30 fs/fat/inode.c:209
 read_pages+0xa3/0x480 mm/readahead.c:160
 page_cache_ra_unbounded+0x347/0x380 mm/readahead.c:297
 do_page_cache_ra mm/readahead.c:327 [inline]
 page_cache_ra_order+0x102/0x120 mm/readahead.c:532
 do_sync_mmap_readahead+0x249/0x280 mm/filemap.c:3271
 filemap_fault+0x311/0xb40 mm/filemap.c:3412
 __do_fault+0xbc/0x200 mm/memory.c:5189
 do_shared_fault mm/memory.c:5674 [inline]
 do_fault mm/memory.c:5748 [inline]
 do_pte_missing mm/memory.c:4251 [inline]
 handle_pte_fault mm/memory.c:6089 [inline]
 __handle_mm_fault mm/memory.c:6232 [inline]
 handle_mm_fault+0xd69/0x2be0 mm/memory.c:6401
 do_user_addr_fault+0x3fe/0x1090 arch/x86/mm/fault.c:1387
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
 __put_user_4+0xd/0x20 arch/x86/lib/putuser.S:92
 __sys_socketpair+0xa6/0x430 net/socket.c:1733
 __do_sys_socketpair net/socket.c:1799 [inline]
 __se_sys_socketpair net/socket.c:1796 [inline]
 __x64_sys_socketpair+0x52/0x60 net/socket.c:1796
 x64_sys_call+0x23f2/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:54
 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 0xffffffff8688c7b0 of 8 bytes by task 23831 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+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
 selinux_netlink_send+0x583/0x5f0 security/selinux/hooks.c:6116
 security_netlink_send+0x40/0x80 security/security.c:4483
 netlink_sendmsg+0x498/0x6b0 net/netlink/af_netlink.c:1873
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x142/0x180 net/socket.c:727
 ____sys_sendmsg+0x31e/0x4e0 net/socket.c:2566
 ___sys_sendmsg+0x17b/0x1d0 net/socket.c:2620
 __sys_sendmsg net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0xd4/0x160 net/socket.c:2655
 x64_sys_call+0x2999/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:47
 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: 0x000000000002e9c0 -> 0x00000000000c8d50

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 23831 Comm: syz.0.4566 Not tainted 6.16.0-rc2-syzkaller-00024-g9afe652958c3 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
SELinux: unrecognized netlink message: protocol=0 nlmsg_type=2582 sclass=netlink_route_socket pid=23831 comm=syz.0.4566
SELinux: unrecognized netlink message: protocol=0 nlmsg_type=2578 sclass=netlink_route_socket pid=23831 comm=syz.0.4566