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BUG: KCSAN: data-race in do_fcntl / vfs_write

write to 0xffff88803698cb40 of 4 bytes by task 28581 on cpu 1:
 setfl fs/fcntl.c:81 [inline]
 do_fcntl+0xc4c/0xc80 fs/fcntl.c:355
 __do_sys_fcntl fs/fcntl.c:471 [inline]
 __se_sys_fcntl+0xc6/0x180 fs/fcntl.c:456
 __x64_sys_fcntl+0x3f/0x50 fs/fcntl.c:456
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88803698cb40 of 4 bytes by task 28586 on cpu 0:
 iocb_flags include/linux/fs.h:3359 [inline]
 init_sync_kiocb include/linux/fs.h:2144 [inline]
 new_sync_write fs/read_write.c:514 [inline]
 vfs_write+0x318/0x7e0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 28586 Comm: syz-executor.1 Tainted: G        W         5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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