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BUG: KCSAN: data-race in dd_has_work / dd_insert_request

write to 0xffff8881037289a8 of 8 bytes by task 1173 on cpu 0:
 __list_add include/linux/list.h:70 [inline]
 list_add_tail include/linux/list.h:100 [inline]
 dd_insert_request+0x27a/0x430 block/mq-deadline.c:521
 dd_insert_requests+0x10c/0x150 block/mq-deadline.c:537
 blk_mq_sched_insert_request+0x228/0x240 block/blk-mq-sched.c:448
 blk_mq_submit_bio+0x8b1/0x1060 block/blk-mq.c:2243
 __submit_bio_noacct_mq block/blk-core.c:1014 [inline]
 submit_bio_noacct+0x7c2/0x9a0 block/blk-core.c:1047
 submit_bio+0x200/0x370 block/blk-core.c:1118
 submit_bh_wbc+0x36b/0x3b0 fs/buffer.c:3055
 submit_bh fs/buffer.c:3061 [inline]
 __sync_dirty_buffer+0x136/0x1e0 fs/buffer.c:3156
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3169
 __ext4_handle_dirty_metadata+0x1d3/0x590 fs/ext4/ext4_jbd2.c:364
 ext4_handle_dirty_dirblock+0x184/0x330 fs/ext4/namei.c:407
 add_dirent_to_buf+0x4a8/0x610 fs/ext4/namei.c:2043
 ext4_add_entry+0x62e/0x21a0 fs/ext4/namei.c:2252
 ext4_add_nondir+0x50/0x1a0 fs/ext4/namei.c:2585
 ext4_symlink+0x533/0x780 fs/ext4/namei.c:3417
 vfs_symlink+0xbe/0x170 fs/namei.c:4176
 do_symlinkat+0x11e/0x2b0 fs/namei.c:4206
 __do_sys_symlink fs/namei.c:4227 [inline]
 __se_sys_symlink fs/namei.c:4225 [inline]
 __x64_sys_symlink+0x32/0x40 fs/namei.c:4225
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881037289a8 of 8 bytes by task 2011 on cpu 1:
 list_empty_careful include/linux/list.h:319 [inline]
 dd_has_work+0xd3/0xe0 block/mq-deadline.c:586
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:135 [inline]
 blk_mq_do_dispatch_sched+0x138/0x610 block/blk-mq-sched.c:199
 __blk_mq_sched_dispatch_requests+0x1fd/0x2a0 block/blk-mq-sched.c:310
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:341
 __blk_mq_run_hw_queue+0xc1/0x140 block/blk-mq.c:1488
 blk_mq_run_work_fn+0x3d/0x50 block/blk-mq.c:1820
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2011 Comm: kworker/1:1H Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kblockd blk_mq_run_work_fn
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