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BUG: KCSAN: data-race in copyout / fat16_ent_put

write to 0xffff88812089555e of 2 bytes by task 32388 on cpu 0:
 fat16_ent_put+0x54/0x90 fs/fat/fatent.c:181
 fat_alloc_clusters+0x4e1/0xbf0 fs/fat/fatent.c:501
 fat_add_cluster+0x3b/0xd0 fs/fat/inode.c:108
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x3c6/0x4f0 fs/fat/inode.c:190
 __block_write_begin_int+0x306/0xf80 fs/buffer.c:2008
 __block_write_begin fs/buffer.c:2058 [inline]
 block_write_begin+0x76/0x160 fs/buffer.c:2117
 cont_write_begin+0x3bd/0x660 fs/buffer.c:2466
 fat_write_begin+0x69/0xc0 fs/fat/inode.c:236
 generic_perform_write+0x13a/0x320 mm/filemap.c:3287
 __generic_file_write_iter+0x240/0x370 mm/filemap.c:3416
 generic_file_write_iter+0x294/0x38e mm/filemap.c:3448
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:483
 __vfs_write+0x9e/0xb0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0xc5/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888120895400 of 1024 bytes by task 32393 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:89 [inline]
 copyout+0x9b/0xb0 lib/iov_iter.c:142
 copy_page_to_iter_iovec lib/iov_iter.c:212 [inline]
 copy_page_to_iter+0x25c/0x910 lib/iov_iter.c:921
 generic_file_buffered_read mm/filemap.c:2122 [inline]
 generic_file_read_iter+0x96a/0x1490 mm/filemap.c:2302
 blkdev_read_iter+0xae/0xe0 fs/block_dev.c:2039
 call_read_iter include/linux/fs.h:1895 [inline]
 new_sync_read+0x306/0x450 fs/read_write.c:414
 __vfs_read+0x9e/0xb0 fs/read_write.c:427
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x13e/0x2b0 fs/read_write.c:446
 ksys_read+0xc5/0x1a0 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+0x49/0x60 fs/read_write.c:595
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 32393 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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