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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff866a0a58 of 8 bytes by task 10916 on cpu 0:
 prb_reserve+0x740/0xb60
 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
 logfc+0x2d1/0x2e0
 fs_param_bad_value fs/fs_parser.c:196 [inline]
 fs_param_is_string+0xa7/0xf0 fs/fs_parser.c:276
 __fs_parse+0x307/0x410 fs/fs_parser.c:129
 fs_parse include/linux/fs_parser.h:76 [inline]
 shmem_parse_one+0x78/0xb60 mm/shmem.c:4601
 vfs_parse_fs_param+0x13b/0x290 fs/fs_context.c:146
 vfs_parse_fs_string fs/fs_context.c:188 [inline]
 vfs_parse_monolithic_sep+0x19b/0x220 fs/fs_context.c:230
 shmem_parse_monolithic+0x24/0x30 mm/shmem.c:4799
 parse_monolithic_mount_data+0x43/0x50 fs/fs_context.c:719
 do_remount fs/namespace.c:3095 [inline]
 path_mount+0x8e7/0xb30 fs/namespace.c:3879
 do_mount fs/namespace.c:3900 [inline]
 __do_sys_mount fs/namespace.c:4111 [inline]
 __se_sys_mount+0x27f/0x2d0 fs/namespace.c:4088
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4088
 x64_sys_call+0x2c84/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:166
 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 0xffffffff866a0a58 of 8 bytes by task 10914 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1957 [inline]
 _prb_read_valid+0x46e/0x6c0 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid_info+0x67/0x90 kernel/printk/printk_ringbuffer.c:2216
 find_first_fitting_seq+0x1bc/0x310 kernel/printk/printk.c:1589
 syslog_print_all+0x11d/0x3c0 kernel/printk/printk.c:1721
 do_syslog+0x431/0x7f0 kernel/printk/printk.c:1799
 __do_sys_syslog kernel/printk/printk.c:1877 [inline]
 __se_sys_syslog kernel/printk/printk.c:1875 [inline]
 __x64_sys_syslog+0x43/0x50 kernel/printk/printk.c:1875
 x64_sys_call+0x29be/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:104
 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: 0x000000000000020b -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10914 Comm: syz.0.2271 Not tainted 6.14.0-rc6-syzkaller-00016-g0fed89a961ea #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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