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BUG: KCSAN: data-race in atime_needs_update / inode_update_timestamps

write to 0xffff888126d2c9ac of 4 bytes by task 26637 on cpu 1:
 inode_set_mtime_to_ts include/linux/fs.h:1658 [inline]
 inode_update_timestamps+0x147/0x270 fs/inode.c:2112
 generic_update_time fs/inode.c:2147 [inline]
 inode_update_time fs/inode.c:2167 [inline]
 file_update_time_flags+0x26c/0x310 fs/inode.c:2394
 file_update_time+0x17/0x20 fs/inode.c:2415
 shmem_file_write_iter+0x9c/0xf0 mm/shmem.c:3463
 iter_file_splice_write+0x66b/0xa20 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888126d2c9ac of 4 bytes by task 26635 on cpu 0:
 inode_get_mtime_nsec include/linux/fs.h:1644 [inline]
 inode_get_mtime include/linux/fs.h:1650 [inline]
 relatime_need_update fs/inode.c:2061 [inline]
 atime_needs_update+0x2a8/0x3e0 fs/inode.c:2207
 touch_atime+0x4a/0x340 fs/inode.c:2222
 file_accessed include/linux/fs.h:2254 [inline]
 shmem_file_splice_read+0x5b1/0x600 mm/shmem.c:3625
 do_splice_read fs/splice.c:982 [inline]
 splice_direct_to_actor+0x26f/0x680 fs/splice.c:1086
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x04fa21b9 -> 0x0588dccb

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 26635 Comm: syz.5.8560 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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