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BUG: KCSAN: data-race in deadline_remove_request / ll_back_merge_fn

read to 0xffff888129d38440 of 8 bytes by task 19993 on cpu 0:
 req_set_nomerge block/blk.h:259 [inline]
 ll_new_hw_segment block/blk-merge.c:583 [inline]
 ll_new_hw_segment block/blk-merge.c:566 [inline]
 ll_back_merge_fn+0xa63/0xd80 block/blk-merge.c:600
 blk_rq_append_bio+0x231/0x450 block/blk-map.c:33
 __blk_rq_map_user_iov block/blk-map.c:89 [inline]
 blk_rq_map_user_iov+0x1a8/0x420 block/blk-map.c:142
 blk_rq_map_user+0x90/0xd0 block/blk-map.c:172
 sg_start_req drivers/scsi/sg.c:1837 [inline]
 sg_common_write.isra.0+0xc64/0x12c0 drivers/scsi/sg.c:807
 sg_new_write.isra.0+0x2bd/0x520 drivers/scsi/sg.c:776
 sg_write.part.0+0x73e/0x8c0 drivers/scsi/sg.c:640
 sg_write+0x65/0x88 drivers/scsi/sg.c:621
 do_loop_readv_writev fs/read_write.c:717 [inline]
 do_loop_readv_writev fs/read_write.c:701 [inline]
 do_iter_write fs/read_write.c:972 [inline]
 do_iter_write+0x34b/0x3c0 fs/read_write.c:951
 vfs_writev+0x118/0x1c0 fs/read_write.c:1015
 do_writev+0xe3/0x250 fs/read_write.c:1058
 __do_sys_writev fs/read_write.c:1131 [inline]
 __se_sys_writev fs/read_write.c:1128 [inline]
 __x64_sys_writev+0x4e/0x60 fs/read_write.c:1128
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888129d38440 of 8 bytes by task 7840 on cpu 1:
 deadline_remove_request+0x1e5/0x260 block/mq-deadline.c:123
 deadline_move_request block/mq-deadline.c:176 [inline]
 __dd_dispatch_request block/mq-deadline.c:365 [inline]
 dd_dispatch_request+0x421/0x500 block/mq-deadline.c:387
 blk_mq_do_dispatch_sched+0x1e3/0x260 block/blk-mq-sched.c:103
 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: 7840 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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