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BUG: KCSAN: data-race in __mod_timer / blk_add_timer

write to 0xffff888101c2ab78 of 8 bytes by task 710 on cpu 0:
 __mod_timer+0x721/0xbe0 kernel/time/timer.c:1052
 mod_timer+0x1b/0x20 kernel/time/timer.c:1108
 blk_mq_timeout_work+0xc9/0x2d0 block/blk-mq.c:984
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffff888101c2ab78 of 8 bytes by task 25604 on cpu 1:
 blk_add_timer+0x125/0x1a0 include/linux/list.h:821
 blk_mq_start_request+0x115/0x1b0 block/blk-mq.c:727
 scsi_queue_rq+0x1295/0x15a0 drivers/scsi/scsi_lib.c:1683
 blk_mq_dispatch_rq_list+0x695/0x1040 block/blk-mq.c:1380
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:201 [inline]
 blk_mq_do_dispatch_sched+0x3b5/0x640 block/blk-mq-sched.c:214
 __blk_mq_sched_dispatch_requests+0x1eb/0x290 block/blk-mq-sched.c:329
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:360
 __blk_mq_run_hw_queue+0xbc/0x140 block/blk-mq.c:1500
 __blk_mq_delay_run_hw_queue+0x163/0x2f0 block/blk-mq.c:1577
 blk_mq_run_hw_queue+0x22c/0x250 block/blk-mq.c:1630
 blk_mq_sched_insert_requests+0x12b/0x1f0 block/blk-mq-sched.c:513
 blk_mq_flush_plug_list+0x2f2/0x3c0 block/blk-mq.c:1955
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1731
 blk_finish_plug+0x44/0x60 block/blk-core.c:1748
 wb_writeback+0x6af/0x700 fs/fs-writeback.c:2087
 wb_check_old_data_flush fs/fs-writeback.c:2155 [inline]
 wb_do_writeback+0x461/0x510 fs/fs-writeback.c:2208
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x000000010002a6c3 -> 0x000000010002b007

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 25604 Comm: kworker/u4:6 Tainted: G        W         5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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