loop4: detected capacity change from 0 to 8192
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BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff8881063bbc20 of 8 bytes by task 3866 on cpu 1:
 mark_buffer_dirty_inode+0x18d/0x1c0 fs/buffer.c:682
 fat_mirror_bhs+0x241/0x330 fs/fat/fatent.c:398
 fat_alloc_clusters+0x994/0xa80 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+0x25c/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x417/0xfa0 fs/buffer.c:2125
 __block_write_begin fs/buffer.c:2174 [inline]
 block_write_begin+0x7b/0x170 fs/buffer.c:2235
 cont_write_begin+0x486/0x6b0 fs/buffer.c:2587
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:229
 cont_expand_zero fs/buffer.c:2514 [inline]
 cont_write_begin+0x186/0x6b0 fs/buffer.c:2577
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:229
 generic_cont_expand_simple+0xaa/0x150 fs/buffer.c:2478
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_fallocate+0x182/0x1d0 fs/fat/file.c:301
 vfs_fallocate+0x392/0x3e0 fs/open.c:334
 ksys_fallocate fs/open.c:357 [inline]
 __do_sys_fallocate fs/open.c:365 [inline]
 __se_sys_fallocate fs/open.c:363 [inline]
 __x64_sys_fallocate+0x79/0xc0 fs/open.c:363
 x64_sys_call+0x2783/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:286
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881063bbc20 of 8 bytes by task 3853 on cpu 0:
 mark_buffer_dirty_inode+0x96/0x1c0 fs/buffer.c:678
 fat_mirror_bhs+0x241/0x330 fs/fat/fatent.c:398
 fat_alloc_clusters+0x994/0xa80 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+0x25c/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x417/0xfa0 fs/buffer.c:2125
 __block_write_begin fs/buffer.c:2174 [inline]
 block_write_begin+0x7b/0x170 fs/buffer.c:2235
 cont_write_begin+0x486/0x6b0 fs/buffer.c:2587
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:229
 generic_perform_write+0x1b4/0x580 mm/filemap.c:4019
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4121
 generic_file_write_iter+0x7d/0x1d0 mm/filemap.c:4147
 iter_file_splice_write+0x5e6/0x970 fs/splice.c:743
 do_splice_from fs/splice.c:941 [inline]
 do_splice+0x99b/0x1150 fs/splice.c:1354
 __do_splice fs/splice.c:1436 [inline]
 __do_sys_splice fs/splice.c:1652 [inline]
 __se_sys_splice+0x24c/0x390 fs/splice.c:1634
 __x64_sys_splice+0x78/0x90 fs/splice.c:1634
 x64_sys_call+0x2945/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:276
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff888106112308

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3853 Comm: syz.4.123 Not tainted 6.11.0-rc6-syzkaller-00026-g88fac17500f4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
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