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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff888120ba3638 of 8 bytes by task 23962 on cpu 0:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x820/0x860 kernel/trace/blktrace.c:271
 blk_add_trace_unplug+0x9f/0xd0 kernel/trace/blktrace.c:954
 trace_block_unplug include/trace/events/block.h:501 [inline]
 blk_mq_flush_plug_list+0x66e/0x6c0 block/blk-mq.c:1732
 blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1768
 blk_mq_make_request+0x65e/0xf60 block/blk-mq.c:1975
 generic_make_request block/blk-core.c:1066 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1008
 submit_bio+0x96/0x3c0 block/blk-core.c:1192
 iomap_dio_submit_bio.isra.0+0xfc/0x120 fs/iomap/direct-io.c:70
 iomap_dio_bio_actor+0x40a/0x960 fs/iomap/direct-io.c:306
 iomap_dio_actor+0x87/0x3a0 fs/iomap/direct-io.c:382
 iomap_apply+0x20d/0x6a0 fs/iomap/apply.c:80
 iomap_dio_rw+0x67e/0x9a0 fs/iomap/direct-io.c:498
 ext4_dio_write_iter fs/ext4/file.c:438 [inline]
 ext4_file_write_iter+0xc38/0xd40 fs/ext4/file.c:545
 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

write to 0xffff888120ba3638 of 8 bytes by task 23957 on cpu 1:
 relay_switch_subbuf+0x478/0x490 kernel/relay.c:790
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x820/0x860 kernel/trace/blktrace.c:271
 blk_add_trace_unplug+0x9f/0xd0 kernel/trace/blktrace.c:954
 trace_block_unplug include/trace/events/block.h:501 [inline]
 blk_mq_flush_plug_list+0x66e/0x6c0 block/blk-mq.c:1732
 blk_flush_plug_list+0x271/0x2a0 block/blk-core.c:1768
 blk_mq_make_request+0x65e/0xf60 block/blk-mq.c:1975
 generic_make_request block/blk-core.c:1066 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1008
 submit_bio+0x96/0x3c0 block/blk-core.c:1192
 iomap_dio_submit_bio.isra.0+0xfc/0x120 fs/iomap/direct-io.c:70
 iomap_dio_bio_actor+0x40a/0x960 fs/iomap/direct-io.c:306
 iomap_dio_actor+0x87/0x3a0 fs/iomap/direct-io.c:382
 iomap_apply+0x20d/0x6a0 fs/iomap/apply.c:80
 iomap_dio_rw+0x67e/0x9a0 fs/iomap/direct-io.c:498
 ext4_dio_write_iter fs/ext4/file.c:438 [inline]
 ext4_file_write_iter+0xc38/0xd40 fs/ext4/file.c:545
 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: 23957 Comm: syz-executor.0 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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