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BUG: KCSAN: data-race in fat_alloc_clusters / fat_statfs

write to 0xffff888151dde0ac of 4 bytes by task 12269 on cpu 0:
 fat_alloc_clusters+0x662/0xa80 fs/fat/fatent.c:511
 fat_add_cluster fs/fat/inode.c:107 [inline]
 __fat_get_block fs/fat/inode.c:154 [inline]
 fat_get_block+0x258/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x3fd/0xf90 fs/buffer.c:2151
 block_write_begin fs/buffer.c:2262 [inline]
 cont_write_begin+0x5fc/0x970 fs/buffer.c:2601
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
 generic_perform_write+0x181/0x490 mm/filemap.c:4112
 __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4229
 generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4255
 do_iter_readv_writev+0x41e/0x4c0 fs/read_write.c:-1
 vfs_writev+0x2df/0x8b0 fs/read_write.c:1057
 do_pwritev fs/read_write.c:1153 [inline]
 __do_sys_pwritev2 fs/read_write.c:1211 [inline]
 __se_sys_pwritev2+0xfc/0x1c0 fs/read_write.c:1202
 __x64_sys_pwritev2+0x67/0x80 fs/read_write.c:1202
 x64_sys_call+0x1cea/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888151dde0ac of 4 bytes by task 12275 on cpu 1:
 fat_statfs+0x166/0x200 fs/fat/inode.c:842
 statfs_by_dentry fs/statfs.c:66 [inline]
 vfs_statfs+0xc5/0x1c0 fs/statfs.c:90
 user_statfs+0x71/0x110 fs/statfs.c:105
 __do_sys_statfs fs/statfs.c:193 [inline]
 __se_sys_statfs fs/statfs.c:190 [inline]
 __x64_sys_statfs+0x65/0xf0 fs/statfs.c:190
 x64_sys_call+0x1edd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:138
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00001f6c -> 0x00001f6b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12275 Comm: syz.5.2818 Not tainted 6.16.0-rc5-syzkaller-00266-g3f31a806a62e #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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