==================================================================
BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff888121551670 of 8 bytes by task 20350 on cpu 0:
 mark_buffer_dirty_inode+0x18d/0x1c0 fs/buffer.c:684
 fat_mirror_bhs+0x247/0x340 fs/fat/fatent.c:398
 fat_alloc_clusters+0x994/0xa80 fs/fat/fatent.c:543
 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+0x417/0xfa0 fs/buffer.c:2105
 __block_write_begin fs/buffer.c:2154 [inline]
 block_write_begin+0x7b/0x170 fs/buffer.c:2213
 cont_write_begin+0x486/0x6b0 fs/buffer.c:2567
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 cont_expand_zero fs/buffer.c:2494 [inline]
 cont_write_begin+0x186/0x6b0 fs/buffer.c:2557
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_perform_write+0x1d5/0x410 mm/filemap.c:3974
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4069
 generic_file_write_iter+0x7d/0x1d0 mm/filemap.c:4095
 do_iter_readv_writev+0x339/0x3e0
 vfs_writev+0x2e9/0x860 fs/read_write.c:971
 do_pwritev fs/read_write.c:1072 [inline]
 __do_sys_pwritev2 fs/read_write.c:1131 [inline]
 __se_sys_pwritev2+0x10c/0x1d0 fs/read_write.c:1122
 __x64_sys_pwritev2+0x78/0x90 fs/read_write.c:1122
 x64_sys_call+0xf52/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888121551670 of 8 bytes by task 20432 on cpu 1:
 mark_buffer_dirty_inode+0x96/0x1c0 fs/buffer.c:680
 fat_mirror_bhs+0x247/0x340 fs/fat/fatent.c:398
 fat_alloc_clusters+0x994/0xa80 fs/fat/fatent.c:543
 fat_add_cluster+0x47/0xe0 fs/fat/inode.c:108
 fat_fallocate+0x129/0x1d0 fs/fat/file.c:292
 vfs_fallocate+0x380/0x3e0 fs/open.c:330
 do_vfs_ioctl+0x1481/0x1560 fs/ioctl.c:883
 __do_sys_ioctl fs/ioctl.c:902 [inline]
 __se_sys_ioctl+0x81/0x150 fs/ioctl.c:890
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:890
 x64_sys_call+0x155d/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff8881052d8e30

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 20432 Comm: syz-executor.2 Tainted: G        W          6.9.0-rc3-syzkaller-00344-g8f2c057754b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
==================================================================