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BUG: KCSAN: data-race in blk_add_timer / enqueue_timer

write to 0xffff88812a81c820 of 8 bytes by task 2499 on cpu 0:
 hlist_add_head include/linux/list.h:789 [inline]
 enqueue_timer+0x9c/0x210 kernel/time/timer.c:540
 __internal_add_timer+0x4f/0x60 kernel/time/timer.c:553
 internal_add_timer kernel/time/timer.c:595 [inline]
 __mod_timer kernel/time/timer.c:1053 [inline]
 mod_timer+0x303/0x7a0 kernel/time/timer.c:1100
 blk_add_timer+0x1c6/0x1d0 block/blk-timeout.c:148
 blk_mq_start_request+0xb7/0x370 block/blk-mq.c:659
 scsi_mq_prep_fn drivers/scsi/scsi_lib.c:1601 [inline]
 scsi_queue_rq+0xb59/0x1800 drivers/scsi/scsi_lib.c:1671
 blk_mq_dispatch_rq_list+0xbe9/0xe40 block/blk-mq.c:1238
 blk_mq_do_dispatch_sched+0x11d/0x260 block/blk-mq-sched.c:115
 blk_mq_sched_dispatch_requests+0x2b4/0x380 block/blk-mq-sched.c:211
 __blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1368
 blk_mq_run_work_fn+0x57/0x70 block/blk-mq.c:1597
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88812a81c820 of 8 bytes by task 7936 on cpu 1:
 blk_add_timer+0x138/0x1d0 block/blk-timeout.c:136
 blk_mq_start_request+0xb7/0x370 block/blk-mq.c:659
 scsi_mq_prep_fn drivers/scsi/scsi_lib.c:1601 [inline]
 scsi_queue_rq+0xb59/0x1800 drivers/scsi/scsi_lib.c:1671
 blk_mq_dispatch_rq_list+0xbe9/0xe40 block/blk-mq.c:1238
 blk_mq_do_dispatch_sched+0x11d/0x260 block/blk-mq-sched.c:115
 blk_mq_sched_dispatch_requests+0x2b4/0x380 block/blk-mq-sched.c:211
 __blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1368
 __blk_mq_delay_run_hw_queue+0x31b/0x3a0 block/blk-mq.c:1436
 blk_mq_run_hw_queue+0xfd/0x1c0 block/blk-mq.c:1473
 blk_mq_sched_insert_requests+0x198/0x260 block/blk-mq-sched.c:444
 blk_mq_flush_plug_list+0x572/0x6c0 block/blk-mq.c:1733
 blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1768
 blk_finish_plug block/blk-core.c:1785 [inline]
 blk_finish_plug+0x60/0x84 block/blk-core.c:1781
 ext4_writepages+0xe32/0x2500 fs/ext4/inode.c:2832
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1c5/0x230 mm/filemap.c:421
 file_write_and_wait_range+0xfd/0x160 mm/filemap.c:782
 ext4_sync_file+0x266/0xaf0 fs/ext4/fsync.c:153
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2856 [inline]
 ext4_buffered_write_iter+0x222/0x290 fs/ext4/file.c:259
 ext4_file_write_iter+0xf4/0xd40 fs/ext4/file.c:547
 call_write_iter include/linux/fs.h:1902 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7936 Comm: rs:main Q:Reg Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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