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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8880a1537238 of 8 bytes by task 21377 on cpu 1:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x801/0x840 kernel/trace/blktrace.c:272
 blk_add_trace_bio.isra.0+0x12f/0x150 kernel/trace/blktrace.c:865
 blk_add_trace_getrq+0x51/0xa0 kernel/trace/blktrace.c:910
 trace_block_getrq include/trace/events/block.h:423 [inline]
 blk_mq_make_request+0x7ff/0xf60 block/blk-mq.c:1982
 generic_make_request block/blk-core.c:1064 [inline]
 generic_make_request+0x196/0x740 block/blk-core.c:1006
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 dio_bio_submit fs/direct-io.c:481 [inline]
 dio_send_cur_page fs/direct-io.c:807 [inline]
 submit_page_section fs/direct-io.c:874 [inline]
 do_direct_IO fs/direct-io.c:1088 [inline]
 do_blockdev_direct_IO+0x5425/0x78c0 fs/direct-io.c:1326
 __blockdev_direct_IO+0x86/0xa0 fs/direct-io.c:1412
 ext4_direct_IO_write fs/ext4/inode.c:3742 [inline]
 ext4_direct_IO+0x76c/0xfb0 fs/ext4/inode.c:3871
 generic_file_direct_write+0x14d/0x2e0 mm/filemap.c:3208
 __generic_file_write_iter+0x17e/0x380 mm/filemap.c:3391
 ext4_file_write_iter+0x1bd/0xa00 fs/ext4/file.c:268
 call_write_iter include/linux/fs.h:1895 [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/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880a1537238 of 8 bytes by task 21373 on cpu 0:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x801/0x840 kernel/trace/blktrace.c:272
 blk_add_trace_rq+0x15b/0x1a0 kernel/trace/blktrace.c:813
 blk_add_trace_rq_issue+0xec/0x100 kernel/trace/blktrace.c:827
 trace_block_rq_issue include/trace/events/block.h:207 [inline]
 blk_mq_start_request+0x21f/0x370 block/blk-mq.c:682
 scsi_mq_prep_fn drivers/scsi/scsi_lib.c:1602 [inline]
 scsi_queue_rq+0x943/0x1850 drivers/scsi/scsi_lib.c:1672
 blk_mq_dispatch_rq_list+0xbe9/0xe40 block/blk-mq.c:1273
 blk_mq_do_dispatch_sched+0x11d/0x260 block/blk-mq-sched.c:115
 blk_mq_sched_dispatch_requests+0x2b4/0x380 block/blk-mq-sched.c:211
 __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_mq_make_request+0x65e/0xf60 block/blk-mq.c:2014
 generic_make_request block/blk-core.c:1064 [inline]
 generic_make_request+0x196/0x740 block/blk-core.c:1006
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 dio_bio_submit fs/direct-io.c:481 [inline]
 dio_send_cur_page fs/direct-io.c:807 [inline]
 submit_page_section fs/direct-io.c:874 [inline]
 do_direct_IO fs/direct-io.c:1088 [inline]
 do_blockdev_direct_IO+0x5425/0x78c0 fs/direct-io.c:1326
 __blockdev_direct_IO+0x86/0xa0 fs/direct-io.c:1412
 ext4_direct_IO_write fs/ext4/inode.c:3742 [inline]
 ext4_direct_IO+0x76c/0xfb0 fs/ext4/inode.c:3871
 generic_file_direct_write+0x14d/0x2e0 mm/filemap.c:3208
 __generic_file_write_iter+0x17e/0x380 mm/filemap.c:3391
 ext4_file_write_iter+0x1bd/0xa00 fs/ext4/file.c:268
 call_write_iter include/linux/fs.h:1895 [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/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 21373 Comm: syz-executor.2 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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