syzbot

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BUG: KCSAN: data-race in shmem_file_splice_read / shmem_file_splice_read

write to 0xffff888103ff7828 of 8 bytes by task 1895 on cpu 0:
 shmem_file_splice_read+0x470/0x600 mm/shmem.c:3650
 do_splice_read fs/splice.c:982 [inline]
 splice_direct_to_actor+0x26e/0x670 fs/splice.c:1086
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1230
 do_sendfile+0x382/0x650 fs/read_write.c:1372
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64 fs/read_write.c:1419 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
 x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff888103ff7828 of 8 bytes by task 1896 on cpu 1:
 shmem_file_splice_read+0x470/0x600 mm/shmem.c:3650
 do_splice_read fs/splice.c:982 [inline]
 splice_direct_to_actor+0x26e/0x670 fs/splice.c:1086
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1230
 do_sendfile+0x382/0x650 fs/read_write.c:1372
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64 fs/read_write.c:1419 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
 x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000008fa6 -> 0x0000000000008fee

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 1896 Comm: syz.9.9165 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
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