==================================================================
BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8881217d1638 of 8 bytes by interrupt 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_rq+0x15b/0x1a0 kernel/trace/blktrace.c:813
 blk_add_trace_rq_complete+0xf4/0x110 kernel/trace/blktrace.c:842
 trace_block_rq_complete include/trace/events/block.h:116 [inline]
 blk_update_request+0x232/0x7b0 block/blk-core.c:1435
 scsi_end_request+0x6b/0x3e0 drivers/scsi/scsi_lib.c:579
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:963
 scsi_finish_command+0x280/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1477
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x19
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:756 [inline]
 kcsan_setup_watchpoint+0x1d4/0x460 kernel/kcsan/core.c:436
 check_access kernel/kcsan/core.c:466 [inline]
 __tsan_write4 kernel/kcsan/core.c:595 [inline]
 __tsan_unaligned_write4+0xc4/0x100 kernel/kcsan/core.c:595
 __rcu_read_lock+0x3c/0x50 kernel/rcu/tree_plugin.h:358
 rcu_read_lock include/linux/rcupdate.h:597 [inline]
 batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:407 [inline]
 batadv_nc_worker+0xa2/0x390 net/batman-adv/network-coding.c:718
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff8881217d1638 of 8 bytes by task 7688 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_bio.isra.0+0x12f/0x150 kernel/trace/blktrace.c:865
 blk_add_trace_bio_queue+0x3d/0x50 kernel/trace/blktrace.c:902
 trace_block_bio_queue include/trace/events/block.h:357 [inline]
 generic_make_request_checks+0xf34/0x1130 block/blk-core.c:966
 generic_make_request+0x3e/0x740 block/blk-core.c:1018
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 submit_bh_wbc+0x40f/0x460 fs/buffer.c:3095
 __block_write_full_page+0x4e9/0x870 fs/buffer.c:1767
 block_write_full_page+0x1c0/0x1e0 fs/buffer.c:2953
 blkdev_writepage+0x2e/0x40 fs/block_dev.c:609
 __writepage+0x40/0xb0 mm/page-writeback.c:2303
 write_cache_pages+0x47a/0xb40 mm/page-writeback.c:2238
 generic_writepages mm/page-writeback.c:2329 [inline]
 generic_writepages+0x79/0xc0 mm/page-writeback.c:2318
 blkdev_writepages+0x27/0x40 fs/block_dev.c:2031
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaf/0x8e0 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1716
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1785
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1894
 wb_check_background_flush fs/fs-writeback.c:1962 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x696/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7688 Comm: kworker/u4:4 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================