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BUG: KCSAN: data-race in atime_needs_update / ext4_truncate

write to 0xffff888125dc8310 of 16 bytes by task 9386 on cpu 0:
 ext4_truncate+0x611/0x990 fs/ext4/inode.c:4533
 ext4_setattr+0xfb4/0x1620 fs/ext4/inode.c:5665
 notify_change+0x7e1/0xaa0 fs/attr.c:337
 do_truncate+0xfb/0x180 fs/open.c:64
 handle_truncate fs/namei.c:2998 [inline]
 do_last fs/namei.c:3414 [inline]
 path_openat+0x2f48/0x36e0 fs/namei.c:3525
 do_filp_open+0x11e/0x1b0 fs/namei.c:3555
 do_sys_open+0x3b3/0x4f0 fs/open.c:1097
 ksys_open include/linux/syscalls.h:1385 [inline]
 __do_sys_creat fs/open.c:1155 [inline]
 __se_sys_creat fs/open.c:1153 [inline]
 __x64_sys_creat+0x45/0x60 fs/open.c:1153
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125dc8310 of 8 bytes by task 9378 on cpu 1:
 relatime_need_update fs/inode.c:1628 [inline]
 atime_needs_update+0x1ea/0x360 fs/inode.c:1721
 touch_atime+0x63/0x190 fs/inode.c:1736
 file_accessed include/linux/fs.h:2202 [inline]
 generic_file_splice_read+0x4e7/0x500 fs/splice.c:310
 do_splice_to+0xf2/0x130 fs/splice.c:877
 splice_direct_to_actor+0x1a1/0x510 fs/splice.c:954
 do_splice_direct+0x161/0x1e0 fs/splice.c:1063
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1525 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0x12a/0x140 fs/read_write.c:1511
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9378 Comm: syz-executor.2 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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