loop2: detected capacity change from 0 to 2048
==================================================================
BUG: KCSAN: data-race in find_get_block_common / has_bh_in_lru

read-write to 0xffff888237d275e0 of 8 bytes by task 11130 on cpu 1:
 bh_lru_install fs/buffer.c:1256 [inline]
 find_get_block_common+0x45c/0x870 fs/buffer.c:1321
 bdev_getblk+0x4c/0x3c0 include/linux/gfp.h:-1
 __getblk include/linux/buffer_head.h:378 [inline]
 sb_getblk include/linux/buffer_head.h:384 [inline]
 __ext4_get_inode_loc+0x311/0x930 fs/ext4/inode.c:4899
 ext4_get_inode_loc fs/ext4/inode.c:5027 [inline]
 ext4_reserve_inode_write+0xd7/0x250 fs/ext4/inode.c:6462
 __ext4_mark_inode_dirty+0x8c/0x3d0 fs/ext4/inode.c:6640
 ext4_dirty_inode+0x92/0xc0 fs/ext4/inode.c:6677
 __mark_inode_dirty+0x164/0x700 fs/fs-writeback.c:2729
 generic_update_time fs/inode.c:2253 [inline]
 file_update_time_flags+0x299/0x2d0 fs/inode.c:2483
 file_update_time+0x17/0x20 fs/inode.c:2504
 ext4_page_mkwrite+0x15d/0xa90 fs/ext4/inode.c:6843
 do_page_mkwrite mm/memory.c:3684 [inline]
 do_shared_fault mm/memory.c:5936 [inline]
 do_fault mm/memory.c:5998 [inline]
 do_pte_missing mm/memory.c:4566 [inline]
 handle_pte_fault mm/memory.c:6379 [inline]
 __handle_mm_fault mm/memory.c:6517 [inline]
 handle_mm_fault+0x1b3d/0x2da0 mm/memory.c:6686
 do_user_addr_fault+0x634/0x1060 arch/x86/mm/fault.c:1343
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595

read to 0xffff888237d275e0 of 8 bytes by task 11144 on cpu 0:
 has_bh_in_lru+0x35/0x1f0 fs/buffer.c:1462
 smp_call_function_many_cond+0x297/0xb60 kernel/smp.c:856
 on_each_cpu_cond_mask+0x3c/0x80 kernel/smp.c:1077
 on_each_cpu_cond include/linux/smp.h:106 [inline]
 invalidate_bh_lrus+0x2a/0x30 fs/buffer.c:1471
 kill_bdev block/bdev.c:90 [inline]
 set_blocksize+0x1e3/0x270 block/bdev.c:207
 sb_set_blocksize+0x93/0x170 block/bdev.c:240
 fat_fill_super+0x83e/0x1c50 fs/fat/inode.c:1668
 msdos_fill_super+0x24/0x30 fs/fat/namei_msdos.c:662
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1887
 get_tree_bdev+0x1f/0x30 fs/super.c:1910
 msdos_get_tree+0x1c/0x30 fs/fat/namei_msdos.c:667
 vfs_get_tree+0x57/0x1d0 fs/super.c:1947
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3772 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3848
 path_mount+0x4ad/0xb90 fs/namespace.c:4168
 do_mount fs/namespace.c:4181 [inline]
 __do_sys_mount fs/namespace.c:4397 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4374
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4374
 x64_sys_call+0x2bb4/0x3050 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff888100727420

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 11144 Comm: syz.2.1493 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================
FAT-fs (loop2): error, fat_get_cluster: detected the cluster chain loop (i_pos 1)
FAT-fs (loop2): Filesystem has been set read-only