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BUG: KCSAN: data-race in blk_mq_request_bypass_insert / blk_mq_run_hw_queue

write to 0xffff888128e30410 of 8 bytes by task 3219 on cpu 1:
 __list_add include/linux/list.h:70 [inline]
 list_add include/linux/list.h:86 [inline]
 blk_mq_request_bypass_insert+0x6a/0x130 block/blk-mq.c:1742
 blk_mq_sched_insert_request+0x1b4/0x330 block/blk-mq-sched.c:479
 blk_mq_requeue_work+0x38b/0x490 block/blk-mq.c:771
 process_one_work+0x3cb/0x990 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffff888128e30410 of 8 bytes by task 8795 on cpu 0:
 list_empty_careful include/linux/list.h:301 [inline]
 blk_mq_hctx_has_pending block/blk-mq.c:70 [inline]
 blk_mq_run_hw_queue+0x11a/0x240 block/blk-mq.c:1544
 blk_mq_sched_insert_request+0x2ae/0x330 block/blk-mq-sched.c:496
 blk_mq_make_request+0x672/0x1010 block/blk-mq.c:2106
 do_make_request block/blk-core.c:1084 [inline]
 generic_make_request+0x240/0x5c0 block/blk-core.c:1156
 submit_bio+0x200/0x370 block/blk-core.c:1275
 submit_bh_wbc+0x34e/0x390 fs/buffer.c:3073
 submit_bh fs/buffer.c:3079 [inline]
 __sync_dirty_buffer+0xfa/0x170 fs/buffer.c:3165
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3178
 __ext4_handle_dirty_metadata+0x186/0x540 fs/ext4/ext4_jbd2.c:339
 ext4_handle_dirty_dirblock+0x184/0x330 fs/ext4/namei.c:411
 ext4_delete_entry+0x227/0x340 fs/ext4/namei.c:2527
 ext4_unlink+0x588/0x9e0 fs/ext4/namei.c:3225
 vfs_unlink+0x22f/0x3d0 fs/namei.c:3825
 do_unlinkat+0x28a/0x4d0 fs/namei.c:3889
 __do_sys_unlink fs/namei.c:3936 [inline]
 __se_sys_unlink fs/namei.c:3934 [inline]
 __x64_sys_unlink+0x2c/0x30 fs/namei.c:3934
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8795 Comm: syz-executor.1 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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