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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86cc6dc0 of 88 bytes by task 3283 on cpu 0:
 prb_reserve+0x6fb/0xaf0 kernel/printk/printk_ringbuffer.c:1693
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 printk_stack_address arch/x86/kernel/dumpstack.c:70 [inline]
 __show_trace_log_lvl+0x460/0x560 arch/x86/kernel/dumpstack.c:282
 __dump_stack+0x1d/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x95/0xd0 lib/dump_stack.c:120
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x25e/0x270 lib/fault-inject.c:174
 should_failslab+0x8c/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4539 [inline]
 slab_alloc_node mm/slub.c:4897 [inline]
 kmem_cache_alloc_node_noprof+0x85/0x3d0 mm/slub.c:4989
 __alloc_skb+0x2db/0x6f0 net/core/skbuff.c:704
 alloc_skb_fclone include/linux/skbuff.h:1434 [inline]
 tcp_stream_alloc_skb+0x30/0x320 net/ipv4/tcp.c:931
 tcp_sendmsg_locked+0xd2f/0x2c70 net/ipv4/tcp.c:1256
 tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1451
 inet_sendmsg+0x76/0xd0 net/ipv4/af_inet.c:865
 sock_sendmsg_nosec net/socket.c:776 [inline]
 __sock_sendmsg net/socket.c:790 [inline]
 sock_write_iter+0x2a4/0x2f0 net/socket.c:1241
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57d/0x990 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 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 0xffffffff86cc6dc0 of 8 bytes by task 4339 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:500 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2017 [inline]
 _prb_read_valid+0x325/0x930 kernel/printk/printk_ringbuffer.c:2174
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2245
 printk_get_next_message+0xea/0x550 kernel/printk/printk.c:3052
 console_emit_next_record kernel/printk/printk.c:3137 [inline]
 console_flush_one_record kernel/printk/printk.c:3269 [inline]
 console_flush_all+0x2bc/0x6b0 kernel/printk/printk.c:3343
 __console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
 console_unlock+0xa1/0x280 kernel/printk/printk.c:3413
 vprintk_emit+0x3e4/0x600 kernel/printk/printk.c:2479
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 fail_dump lib/fault-inject.c:66 [inline]
 should_fail_ex+0x246/0x270 lib/fault-inject.c:174
 should_failslab+0x8c/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4539 [inline]
 slab_alloc_node mm/slub.c:4897 [inline]
 kmem_cache_alloc_lru_noprof+0x81/0x3d0 mm/slub.c:4950
 xas_nomem+0xd1/0x130 lib/xarray.c:309
 shmem_add_to_page_cache+0x3f0/0x5b0 mm/shmem.c:939
 shmem_alloc_and_add_folio mm/shmem.c:1985 [inline]
 shmem_get_folio_gfp+0x517/0xd90 mm/shmem.c:2512
 shmem_get_folio mm/shmem.c:2618 [inline]
 shmem_write_begin+0xfc/0x1f0 mm/shmem.c:3249
 generic_perform_write+0x186/0x490 mm/filemap.c:4358
 shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3424
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57d/0x990 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 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: 0x0000000000016932 -> 0x0000000000018932

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4339 Comm: syz.1.248 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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