syzbot

loop6: detected capacity change from 0 to 8192
==================================================================
BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff888119d9aa18 of 8 bytes by task 8687 on cpu 1:
 mark_buffer_dirty_inode+0x18c/0x1c0 fs/buffer.c:693
 fat_mirror_bhs+0x234/0x320 fs/fat/fatent.c:398
 fat_alloc_clusters+0x98b/0xa80 fs/fat/fatent.c:543
 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+0x400/0xf90 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
 cont_expand_zero fs/buffer.c:2528 [inline]
 cont_write_begin+0x1b0/0x970 fs/buffer.c:2591
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
 generic_perform_write+0x184/0x490 mm/filemap.c:4112
 __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4229
 generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4255
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x4a0/0x8e0 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0xfd/0x150 fs/read_write.c:798
 x64_sys_call+0xe45/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:19
 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 0xffff888119d9aa18 of 8 bytes by task 8677 on cpu 0:
 mark_buffer_dirty_inode+0x95/0x1c0 fs/buffer.c:689
 fat_mirror_bhs+0x234/0x320 fs/fat/fatent.c:398
 fat_alloc_clusters+0x98b/0xa80 fs/fat/fatent.c:543
 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+0x400/0xf90 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+0x184/0x490 mm/filemap.c:4112
 __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4229
 generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4255
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x4a0/0x8e0 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2cdd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:2
 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: 0x0000000000000000 -> 0xffff888106ab6908

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8677 Comm: syz.6.15080 Not tainted 6.16.0-rc2-syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================