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BUG: KCSAN: data-race in copyout / fat16_ent_put

write to 0xffff88811bfd9088 of 2 bytes by task 11825 on cpu 0:
 fat16_ent_put+0x5b/0x90 fs/fat/fatent.c:181
 fat_ent_write+0x6d/0xf0 fs/fat/fatent.c:415
 fat_chain_add+0x34e/0x400 fs/fat/misc.c:130
 fat_add_cluster+0x92/0xd0 fs/fat/inode.c:113
 fat_fallocate+0x152/0x1f0 fs/fat/file.c:291
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ioctl_preallocate+0x12b/0x190 fs/ioctl.c:504
 file_ioctl fs/ioctl.c:544 [inline]
 do_vfs_ioctl+0xa73/0xd00 fs/ioctl.c:742
 ksys_ioctl+0xbd/0x150 fs/ioctl.c:761
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:770
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811bfd9000 of 1024 bytes by task 11828 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:89 [inline]
 copyout+0xa8/0xc0 lib/iov_iter.c:142
 copy_page_to_iter_iovec lib/iov_iter.c:212 [inline]
 copy_page_to_iter+0x252/0x8e0 lib/iov_iter.c:921
 generic_file_buffered_read mm/filemap.c:2122 [inline]
 generic_file_read_iter+0x978/0x1440 mm/filemap.c:2302
 blkdev_read_iter+0xb2/0xe0 fs/block_dev.c:2039
 call_read_iter include/linux/fs.h:1895 [inline]
 new_sync_read+0x389/0x4f0 fs/read_write.c:414
 __vfs_read+0xb1/0xc0 fs/read_write.c:427
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x143/0x2c0 fs/read_write.c:446
 ksys_read+0xd5/0x1b0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x4c/0x60 fs/read_write.c:595
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11828 Comm: blkid Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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