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BUG: KCSAN: data-race in fat_alloc_clusters / fat_statfs

write to 0xffff88812c8740ac of 4 bytes by task 25576 on cpu 1:
 fat_alloc_clusters+0x634/0xa60 fs/fat/fatent.c:511
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x25c/0x5e0 fs/fat/inode.c:190
 __block_write_begin_int+0x3c3/0xf50 fs/buffer.c:2120
 __block_write_begin fs/buffer.c:2169 [inline]
 block_write_begin+0x7b/0x170 fs/buffer.c:2228
 cont_write_begin+0x479/0x690 fs/buffer.c:2585
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_perform_write+0x1c9/0x410 mm/filemap.c:3969
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4064
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4090
 call_write_iter include/linux/fs.h:1956 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x4ab/0x7d0 fs/read_write.c:584
 ksys_write+0xeb/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:646
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88812c8740ac of 4 bytes by task 25591 on cpu 0:
 fat_statfs+0x168/0x200 fs/fat/inode.c:837
 statfs_by_dentry fs/statfs.c:66 [inline]
 vfs_statfs fs/statfs.c:90 [inline]
 fd_statfs+0xf8/0x220 fs/statfs.c:120
 __do_sys_fstatfs fs/statfs.c:216 [inline]
 __se_sys_fstatfs fs/statfs.c:213 [inline]
 __x64_sys_fstatfs+0x62/0xf0 fs/statfs.c:213
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00001f1c -> 0x00001f1b

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25591 Comm: syz-executor.3 Not tainted 6.6.0-rc7-syzkaller-00195-g2af9b20dbb39 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
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