==================================================================
BUG: KCSAN: data-race in find_get_block_common / has_bh_in_lru

read-write to 0xffff888237d277a0 of 8 bytes by task 27650 on cpu 1:
 bh_lru_install fs/buffer.c:1235 [inline]
 find_get_block_common+0x459/0x870 fs/buffer.c:1300
 bdev_getblk+0x4d/0x3f0 include/linux/gfp.h:-1
 __getblk include/linux/buffer_head.h:380 [inline]
 sb_getblk include/linux/buffer_head.h:386 [inline]
 fat_mirror_bhs+0x149/0x330 fs/fat/fatent.c:392
 fat_alloc_clusters+0xb48/0xc50 fs/fat/fatent.c:548
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x25e/0x5f0 fs/fat/inode.c:190
 __block_write_begin_int+0x400/0xf90 fs/buffer.c:2035
 block_write_begin fs/buffer.c:2146 [inline]
 cont_write_begin+0x5fe/0x970 fs/buffer.c:2484
 fat_write_begin+0x52/0xe0 fs/fat/inode.c:230
 generic_perform_write+0x183/0x490 mm/filemap.c:4325
 __generic_file_write_iter+0x9e/0x120 mm/filemap.c:4442
 generic_file_write_iter+0x8d/0x310 mm/filemap.c:4468
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888237d277a0 of 8 bytes by task 27664 on cpu 0:
 has_bh_in_lru+0x35/0x1f0 fs/buffer.c:1441
 cpu_needs_drain mm/swap.c:793 [inline]
 __lru_add_drain_all+0x287/0x450 mm/swap.c:883
 lru_add_drain_all+0x10/0x20 mm/swap.c:899
 invalidate_bdev+0x47/0x70 block/bdev.c:101
 loop_set_status+0x133/0x6a0 drivers/block/loop.c:1246
 loop_set_status64 drivers/block/loop.c:1372 [inline]
 lo_ioctl+0x671/0x13a0 drivers/block/loop.c:1558
 blkdev_ioctl+0x387/0x460 block/ioctl.c:797
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff88811aaa54e0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 27664 Comm: syz.7.4715 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
loop7: detected capacity change from 8192 to 0
FAT-fs (loop7): unable to read inode block for updating (i_pos 1051)
FAT-fs (loop7): unable to read inode block for updating (i_pos 1051)
FAT-fs (loop7): Failed to update on disk inode for unused fallocated blocks, inode could be corrupted. Please run fsck
Buffer I/O error on dev loop7, logical block 0, lost sync page write