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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff888137ca5438 of 8 bytes by task 3504 on cpu 0:
 relay_switch_subbuf+0x39d/0x3b0 kernel/relay.c:711
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x6ba/0x710 kernel/trace/blktrace.c:275
 blk_add_trace_bio_remap+0x177/0x190 kernel/trace/blktrace.c:1027
 trace_block_bio_remap include/trace/events/block.h:479 [inline]
 blk_partition_remap+0x170/0x1b0 block/blk-core.c:610
 submit_bio_noacct+0x365/0x7f0 block/blk-core.c:796
 submit_bio+0xfb/0x110
 ext4_io_submit+0x86/0xa0 fs/ext4/page-io.c:378
 ext4_writepages+0x6cc/0x1d00 fs/ext4/inode.c:2774
 do_writepages+0x1db/0x350 mm/page-writeback.c:2443
 filemap_fdatawrite_wbc+0xd6/0xf0 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 file_write_and_wait_range+0xd6/0x170 mm/filemap.c:779
 ext4_sync_file+0x105/0x6d0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2744 [inline]
 ext4_buffered_write_iter+0x2ec/0x330 fs/ext4/file.c:277
 ext4_file_write_iter+0x2e3/0x1210
 do_iter_readv_writev+0x27b/0x300
 do_iter_write+0x16f/0x5c0 fs/read_write.c:852
 vfs_iter_write+0x4c/0x70 fs/read_write.c:893
 iter_file_splice_write+0x44a/0x7c0 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x660 fs/splice.c:891
 do_splice_direct+0xfb/0x180 fs/splice.c:979
 do_sendfile+0x3ad/0x900 fs/read_write.c:1246
 __do_sys_sendfile64 fs/read_write.c:1305 [inline]
 __se_sys_sendfile64 fs/read_write.c:1297 [inline]
 __x64_sys_sendfile64+0xb9/0x150 fs/read_write.c:1297
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

write to 0xffff888137ca5438 of 8 bytes by task 1406 on cpu 1:
 relay_switch_subbuf+0x39d/0x3b0 kernel/relay.c:711
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x6ba/0x710 kernel/trace/blktrace.c:275
 blk_add_trace_rq kernel/trace/blktrace.c:848 [inline]
 blk_add_trace_rq_insert+0x1be/0x1d0 kernel/trace/blktrace.c:856
 trace_block_rq_insert include/trace/events/block.h:213 [inline]
 dd_insert_request+0x30b/0x570 block/mq-deadline.c:741
 dd_insert_requests+0xfc/0x140 block/mq-deadline.c:778
 blk_mq_sched_insert_requests+0xc0/0x2a0 block/blk-mq-sched.c:477
 blk_mq_dispatch_plug_list+0x1e9/0x2c0 block/blk-mq.c:2648
 blk_mq_flush_plug_list+0x2ea/0x340 block/blk-mq.c:2690
 __blk_flush_plug+0x25a/0x2b0 block/blk-core.c:1219
 blk_finish_plug+0x44/0x60 block/blk-core.c:1243
 jbd2_journal_commit_transaction+0x1a8f/0x3180 fs/jbd2/commit.c:829
 kjournald2+0x253/0x460 fs/jbd2/journal.c:213
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

value changed: 0x0000000000000038 -> 0x0000000000000030

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1406 Comm: jbd2/sda1-8 Not tainted 5.18.0-syzkaller-10037-g7e284070abe5-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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