==================================================================
BUG: KCSAN: data-race in kthread_insert_work / kthread_worker_fn

write to 0xffff888101a26940 of 8 bytes by task 25999 on cpu 1:
 kthread_worker_fn+0x6d/0x4d0 kernel/kthread.c:726
 loop_kthread_worker_fn+0x3e/0x50 drivers/block/loop.c:933
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888101a26940 of 8 bytes by task 25625 on cpu 0:
 kthread_insert_work+0xe4/0x1a0 kernel/kthread.c:912
 kthread_queue_work+0x73/0x90 kernel/kthread.c:936
 loop_queue_rq+0x10d/0x120 drivers/block/loop.c:2018
 blk_mq_dispatch_rq_list+0x628/0x10b0 block/blk-mq.c:1379
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:191 [inline]
 blk_mq_do_dispatch_sched+0x3cb/0x660 block/blk-mq-sched.c:204
 __blk_mq_sched_dispatch_requests+0x21e/0x2c0 block/blk-mq-sched.c:320
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:351
 __blk_mq_run_hw_queue+0xbc/0x140 block/blk-mq.c:1499
 __blk_mq_delay_run_hw_queue+0x163/0x2f0 block/blk-mq.c:1576
 blk_mq_run_hw_queue+0x22c/0x250 block/blk-mq.c:1629
 blk_mq_sched_insert_requests+0x13f/0x200 block/blk-mq-sched.c:503
 blk_mq_flush_plug_list+0x2f5/0x3c0 block/blk-mq.c:1954
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1747
 blk_finish_plug+0x44/0x60 block/blk-core.c:1764
 read_pages+0x2d9/0x530 mm/readahead.c:150
 page_cache_ra_unbounded+0x3c8/0x410 mm/readahead.c:238
 do_page_cache_ra mm/readahead.c:267 [inline]
 force_page_cache_ra+0x246/0x280 mm/readahead.c:299
 page_cache_sync_ra+0xcc/0xe0 mm/readahead.c:573
 page_cache_sync_readahead include/linux/pagemap.h:879 [inline]
 filemap_get_pages mm/filemap.c:2467 [inline]
 filemap_read+0x388/0x1230 mm/filemap.c:2550
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2701
 blkdev_read_iter+0xb9/0xf0 fs/block_dev.c:1730
 call_read_iter include/linux/fs.h:2108 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000000 -> 0xffff88812d8e7040

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25625 Comm: systemd-udevd Not tainted 5.13.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================