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BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests

read to 0xffff888129d64d50 of 8 bytes by task 8742 on cpu 0:
 blk_mq_sched_dispatch_requests+0x104/0x380 block/blk-mq-sched.c:181
 __blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1403
 __blk_mq_delay_run_hw_queue+0x31b/0x3a0 block/blk-mq.c:1471
 blk_mq_run_hw_queue+0x103/0x1c0 block/blk-mq.c:1508
 blk_mq_sched_insert_requests+0x1ca/0x2e0 block/blk-mq-sched.c:444
 blk_mq_flush_plug_list+0x572/0x6c0 block/blk-mq.c:1772
 blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1766
 blk_finish_plug block/blk-core.c:1783 [inline]
 blk_finish_plug+0x60/0x84 block/blk-core.c:1779
 read_pages+0xbc/0x2d0 mm/readahead.c:142
 __do_page_cache_readahead+0x353/0x390 mm/readahead.c:212
 ra_submit mm/internal.h:62 [inline]
 ondemand_readahead+0x35d/0x710 mm/readahead.c:492
 page_cache_sync_readahead+0x1ad/0x1e0 mm/readahead.c:527
 generic_file_buffered_read mm/filemap.c:2050 [inline]
 generic_file_read_iter+0xeb6/0x1440 mm/filemap.c:2323
 ext4_file_read_iter fs/ext4/file.c:77 [inline]
 ext4_file_read_iter+0xfa/0x240 fs/ext4/file.c:65

write to 0xffff888129d64d50 of 8 bytes by task 8738 on cpu 1:
 blk_mq_sched_dispatch_requests+0x118/0x380 block/blk-mq-sched.c:181
 __blk_mq_run_hw_queue+0xb7/0x160 block/blk-mq.c:1403
 __blk_mq_delay_run_hw_queue+0x31b/0x3a0 block/blk-mq.c:1471
 blk_mq_run_hw_queue+0x103/0x1c0 block/blk-mq.c:1508
 blk_mq_sched_insert_requests+0x1ca/0x2e0 block/blk-mq-sched.c:444
 blk_mq_flush_plug_list+0x572/0x6c0 block/blk-mq.c:1772
 blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1766
 blk_finish_plug block/blk-core.c:1783 [inline]
 blk_finish_plug+0x60/0x84 block/blk-core.c:1779
 do_blockdev_direct_IO+0x48b6/0x78c0 fs/direct-io.c:1355
 __blockdev_direct_IO+0x86/0xa0 fs/direct-io.c:1412
 ext4_direct_IO_write fs/ext4/inode.c:3742 [inline]
 ext4_direct_IO+0x6f5/0xf70 fs/ext4/inode.c:3871
 generic_file_direct_write+0x14d/0x2e0 mm/filemap.c:3207
 __generic_file_write_iter+0x17e/0x380 mm/filemap.c:3390

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8738 Comm: syz-executor.1 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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