syzbot

loop2: 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 0xffff88810621b670 of 8 bytes by task 3084 on cpu 0:
 mark_buffer_dirty_inode+0x18d/0x1c0 fs/buffer.c:682
 fat_mirror_bhs+0x242/0x330 fs/fat/fatent.c:398
 fat_alloc_clusters+0x996/0xa90 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+0x25f/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x419/0xf90 fs/buffer.c:2116
 block_write_begin fs/buffer.c:2227 [inline]
 cont_write_begin+0x548/0x860 fs/buffer.c:2566
 fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
 generic_perform_write+0x189/0x4b0 mm/filemap.c:4103
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4220
 generic_file_write_iter+0x92/0x310 mm/filemap.c:4246
 do_iter_readv_writev+0x40d/0x4b0 fs/read_write.c:-1
 vfs_writev+0x2da/0x880 fs/read_write.c:1055
 do_pwritev fs/read_write.c:1151 [inline]
 __do_sys_pwritev2 fs/read_write.c:1209 [inline]
 __se_sys_pwritev2+0x103/0x1d0 fs/read_write.c:1200
 __x64_sys_pwritev2+0x78/0x90 fs/read_write.c:1200
 x64_sys_call+0x1c86/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810621b670 of 8 bytes by task 3075 on cpu 1:
 mark_buffer_dirty_inode+0x96/0x1c0 fs/buffer.c:678
 fat_mirror_bhs+0x242/0x330 fs/fat/fatent.c:398
 fat_alloc_clusters+0x996/0xa90 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+0x25f/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x419/0xf90 fs/buffer.c:2116
 block_write_begin fs/buffer.c:2227 [inline]
 cont_write_begin+0x548/0x860 fs/buffer.c:2566
 fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
 cont_expand_zero fs/buffer.c:2493 [inline]
 cont_write_begin+0x18d/0x860 fs/buffer.c:2556
 fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
 generic_cont_expand_simple+0xaf/0x150 fs/buffer.c:2457
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_setattr+0x2aa/0x840 fs/fat/file.c:513
 notify_change+0x85c/0x8e0 fs/attr.c:552
 do_truncate fs/open.c:65 [inline]
 do_ftruncate+0x32c/0x440 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+0xa17/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:78
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff8881063cfe08

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3075 Comm: syz.2.9678 Not tainted 6.15.0-rc2-syzkaller-00400-g3088d26962e8 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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