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BUG: KCSAN: data-race in atime_needs_update / fat_truncate_time

write to 0xffff8881259be6d0 of 8 bytes by task 11827 on cpu 0:
 fat_truncate_time+0x246/0x2e0 fs/fat/misc.c:316
 fat_update_time fs/fat/misc.c:330 [inline]
 fat_update_time+0x75/0x1c0 fs/fat/misc.c:322
 update_time fs/inode.c:1683 [inline]
 file_update_time+0x237/0x300 fs/inode.c:1898
 __generic_file_write_iter+0x132/0x380 mm/filemap.c:3384
 generic_file_write_iter+0x28c/0x390 mm/filemap.c:3466
 call_write_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x13b/0x3c0 fs/read_write.c:951
 vfs_iter_write+0x5c/0x80 fs/read_write.c:983
 iter_file_splice_write+0x4c0/0x7f0 fs/splice.c:746
 do_splice_from fs/splice.c:848 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1020
 splice_direct_to_actor+0x215/0x510 fs/splice.c:975
 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

read to 0xffff8881259be6d0 of 8 bytes by task 11823 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_buffered_read mm/filemap.c:2258 [inline]
 generic_file_read_iter+0x116e/0x1440 mm/filemap.c:2324
 call_read_iter include/linux/fs.h:1889 [inline]
 generic_file_splice_read+0x35c/0x500 fs/splice.c:307
 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: 11823 Comm: syz-executor.3 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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