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BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff888106977878 of 8 bytes by task 1341 on cpu 1:
 mark_buffer_dirty_inode+0x18c/0x1c0 fs/buffer.c:695
 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+0x419/0xf70 fs/buffer.c:2151
 block_write_begin fs/buffer.c:2262 [inline]
 cont_write_begin+0x5a3/0x8e0 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+0x198/0x8e0 fs/buffer.c:2591
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
 generic_cont_expand_simple+0xad/0x150 fs/buffer.c:2492
 fat_cont_expand+0x3e/0x170 fs/fat/file.c:223
 fat_setattr+0x2a5/0x8a0 fs/fat/file.c:513
 notify_change+0x806/0x890 fs/attr.c:552
 do_truncate fs/open.c:65 [inline]
 do_ftruncate+0x327/0x430 fs/open.c:192
 do_sys_ftruncate fs/open.c:207 [inline]
 __do_sys_ftruncate fs/open.c:212 [inline]
 __se_sys_ftruncate fs/open.c:210 [inline]
 __x64_sys_ftruncate+0x68/0xc0 fs/open.c:210
 x64_sys_call+0xd65/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:78
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888106977878 of 8 bytes by task 1356 on cpu 0:
 mark_buffer_dirty_inode+0x95/0x1c0 fs/buffer.c:691
 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+0x419/0xf70 fs/buffer.c:2151
 block_write_begin fs/buffer.c:2262 [inline]
 cont_write_begin+0x5a3/0x8e0 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+0x198/0x8e0 fs/buffer.c:2591
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
 generic_cont_expand_simple+0xad/0x150 fs/buffer.c:2492
 fat_cont_expand+0x3e/0x170 fs/fat/file.c:223
 fat_setattr+0x2a5/0x8a0 fs/fat/file.c:513
 notify_change+0x806/0x890 fs/attr.c:552
 do_truncate fs/open.c:65 [inline]
 do_ftruncate+0x327/0x430 fs/open.c:192
 do_sys_ftruncate fs/open.c:207 [inline]
 __do_sys_ftruncate fs/open.c:212 [inline]
 __se_sys_ftruncate fs/open.c:210 [inline]
 __x64_sys_ftruncate+0x68/0xc0 fs/open.c:210
 x64_sys_call+0xd65/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:78
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff888106b62008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 1356 Comm: syz.6.11580 Tainted: G        W           6.15.0-rc4-syzkaller-00021-gca91b9500108 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
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