FAT-fs (loop2): error, clusters badly computed (1020 != 1021)
FAT-fs (loop2): Filesystem has been set read-only
FAT-fs (loop2): error, clusters badly computed (2 != 1022)
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BUG: KCSAN: data-race in __fat_write_inode / fat12_ent_get

write to 0xffff8881189f8234 of 2 bytes by task 22925 on cpu 1:
 fat_set_start fs/fat/fat.h:296 [inline]
 __fat_write_inode+0x36d/0x520 fs/fat/inode.c:878
 fat_write_inode+0x6d/0xf0 fs/fat/inode.c:908
 write_inode fs/fs-writeback.c:1312 [inline]
 __writeback_single_inode+0x6f7/0x8e0 fs/fs-writeback.c:1511
 writeback_single_inode+0x232/0x310 fs/fs-writeback.c:1565
 sync_inode fs/fs-writeback.c:2602 [inline]
 sync_inode_metadata+0x74/0xa0 fs/fs-writeback.c:2622
 __generic_file_fsync+0x122/0x190 fs/libfs.c:1011
 fat_file_fsync+0x58/0x120 fs/fat/file.c:190
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2856 [inline]
 generic_file_write_iter+0x318/0x38c mm/filemap.c:3474
 call_write_iter include/linux/fs.h:1902 [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+0x530/0x840 fs/splice.c:760
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
 splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
 do_splice_direct+0x161/0x1e0 fs/splice.c:1080
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1519 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1511
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881189f8235 of 1 bytes by task 22918 on cpu 0:
 fat12_ent_get+0x84/0x120 fs/fat/fatent.c:125
 fat_ent_read+0x3d0/0x550 fs/fat/fatent.c:370
 fat_get_cluster+0x580/0x980 fs/fat/cache.c:266
 fat_chain_add+0x250/0x400 fs/fat/misc.c:115
 fat_add_cluster+0x92/0xd0 fs/fat/inode.c:112
 fat_fallocate+0x152/0x1f0 fs/fat/file.c:291
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ioctl_preallocate+0x12b/0x190 fs/ioctl.c:491
 file_ioctl fs/ioctl.c:537 [inline]
 do_vfs_ioctl+0xb14/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 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: 0 PID: 22918 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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