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

write to 0xffff8881023490d8 of 8 bytes by task 24 on cpu 1:
 __mod_timer+0x5a1/0x840 kernel/time/timer.c:1126
 mod_timer+0x1f/0x30 kernel/time/timer.c:1195
 blk_mq_timeout_work+0x177/0x340 block/blk-mq.c:1749
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3319
 worker_thread+0x582/0x770 kernel/workqueue.c:3400
 kthread+0x486/0x510 kernel/kthread.c:463
 ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff8881023490d8 of 8 bytes by task 10091 on cpu 0:
 blk_add_timer+0x115/0x1a0 block/blk-timeout.c:-1
 blk_mq_start_request+0x15b/0x3b0 block/blk-mq.c:1357
 loop_queue_rq+0x43/0x680 drivers/block/loop.c:1847
 __blk_mq_issue_directly block/blk-mq.c:2695 [inline]
 blk_mq_request_issue_directly+0x1e6/0x380 block/blk-mq.c:2782
 blk_mq_issue_direct+0x19d/0x530 block/blk-mq.c:2803
 blk_mq_dispatch_queue_requests+0x1fc/0x350 block/blk-mq.c:2878
 blk_mq_flush_plug_list+0x2b6/0x330 block/blk-mq.c:2961
 __blk_flush_plug+0x222/0x2a0 block/blk-core.c:1220
 blk_finish_plug block/blk-core.c:1247 [inline]
 __submit_bio+0x2fc/0x4d0 block/blk-core.c:649
 __submit_bio_noacct_mq block/blk-core.c:722 [inline]
 submit_bio_noacct_nocheck+0x208/0x6a0 block/blk-core.c:751
 submit_bio_noacct+0x6c8/0x8f0 block/blk-core.c:874
 submit_bio+0x2a6/0x2c0 block/blk-core.c:916
 submit_bh_wbc+0x2e0/0x320 fs/buffer.c:2824
 submit_bh fs/buffer.c:2829 [inline]
 __sync_dirty_buffer+0x16b/0x230 fs/buffer.c:2867
 sync_dirty_buffer+0x1a/0x30 fs/buffer.c:2880
 fat_mirror_bhs+0x270/0x320 fs/fat/fatent.c:400
 fat_ent_write+0xd0/0xe0 fs/fat/fatent.c:423
 fat_chain_add+0x15d/0x440 fs/fat/misc.c:136
 fat_add_cluster fs/fat/inode.c:112 [inline]
 __fat_get_block fs/fat/inode.c:154 [inline]
 fat_get_block+0x46c/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x3fd/0xf90 fs/buffer.c:2145
 block_write_begin fs/buffer.c:2256 [inline]
 cont_write_begin+0x5fc/0x970 fs/buffer.c:2594
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:229
 cont_expand_zero fs/buffer.c:2522 [inline]
 cont_write_begin+0x1ad/0x970 fs/buffer.c:2584
 fat_write_begin+0x4f/0xe0 fs/fat/inode.c:229
 generic_cont_expand_simple+0xb0/0x150 fs/buffer.c:2485
 fat_cont_expand+0x3e/0x170 fs/fat/file.c:223
 fat_setattr+0x2a5/0x8a0 fs/fat/file.c:513
 notify_change+0x809/0x890 fs/attr.c:552
 do_truncate fs/open.c:68 [inline]
 do_ftruncate+0x34b/0x450 fs/open.c:195
 do_sys_ftruncate fs/open.c:210 [inline]
 __do_sys_ftruncate fs/open.c:215 [inline]
 __se_sys_ftruncate fs/open.c:213 [inline]
 __x64_sys_ftruncate+0x68/0xc0 fs/open.c:213
 x64_sys_call+0x2d52/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:78
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000ffffcce7 -> 0x00000000ffffd8b7

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10091 Comm: syz.4.2346 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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