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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff88813c361c38 of 8 bytes by task 10951 on cpu 1:
 relay_switch_subbuf+0x399/0x3a0 kernel/relay.c:708
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x665/0x720 kernel/trace/blktrace.c:276
 blk_add_trace_plug+0x4c/0x60 kernel/trace/blktrace.c:950
 trace_block_plug include/trace/events/block.h:405 [inline]
 blk_add_rq_to_plug+0x32d/0x3e0 block/blk-mq.c:1275
 blk_mq_submit_bio+0x692/0xd70 block/blk-mq.c:2994
 __submit_bio+0x11c/0x350 block/blk-core.c:598
 __submit_bio_noacct_mq block/blk-core.c:677 [inline]
 submit_bio_noacct_nocheck+0x449/0x5e0 block/blk-core.c:706
 submit_bio_noacct+0x75c/0x900 block/blk-core.c:805
 submit_bio+0xb7/0xc0 block/blk-core.c:838
 ext4_io_submit+0x8a/0xa0 fs/ext4/page-io.c:378
 ext4_do_writepages+0x731/0x21e0 fs/ext4/inode.c:2634
 ext4_writepages+0x15e/0x2e0 fs/ext4/inode.c:2766
 do_writepages+0x1c5/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:393
 __filemap_fdatawrite_range mm/filemap.c:426 [inline]
 file_write_and_wait_range+0xfa/0x190 mm/filemap.c:784
 ext4_sync_file+0x11f/0x6c0 fs/ext4/fsync.c:159
 vfs_fsync_range+0x111/0x120 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2493 [inline]
 ext4_buffered_write_iter+0x334/0x370 fs/ext4/file.c:305
 ext4_file_write_iter+0x283/0x1230
 do_iter_write+0x4b4/0x7b0 fs/read_write.c:860
 vfs_iter_write+0x56/0x70 fs/read_write.c:901
 iter_file_splice_write+0x462/0x7e0 fs/splice.c:739
 do_splice_from fs/splice.c:934 [inline]
 direct_splice_actor+0x8a/0xb0 fs/splice.c:1143
 splice_direct_to_actor+0x31d/0x690 fs/splice.c:1089
 do_splice_direct+0x10d/0x190 fs/splice.c:1195
 do_sendfile+0x3b6/0x9a0 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffff88813c361c38 of 8 bytes by task 42 on cpu 0:
 relay_switch_subbuf+0x399/0x3a0 kernel/relay.c:708
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x665/0x720 kernel/trace/blktrace.c:276
 blk_add_trace_rq kernel/trace/blktrace.c:844 [inline]
 blk_add_trace_rq_issue+0x1b6/0x1c0 kernel/trace/blktrace.c:857
 trace_block_rq_issue include/trace/events/block.h:227 [inline]
 blk_mq_start_request+0x215/0x270 block/blk-mq.c:1235
 scsi_queue_rq+0x14cc/0x1a30 drivers/scsi/scsi_lib.c:1762
 blk_mq_dispatch_rq_list+0x7b1/0x11b0 block/blk-mq.c:2035
 __blk_mq_sched_dispatch_requests+0x1d4/0xdd0 block/blk-mq-sched.c:301
 blk_mq_sched_dispatch_requests+0x99/0x100 block/blk-mq-sched.c:333
 blk_mq_run_hw_queue+0x29c/0x4c0 block/blk-mq.c:2249
 blk_mq_run_hw_queues+0x161/0x1e0 block/blk-mq.c:2298
 blk_mq_requeue_work+0x408/0x430 block/blk-mq.c:1483
 process_one_work+0x434/0x860 kernel/workqueue.c:2597
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2748
 kthread+0x1d7/0x210 kernel/kthread.c:389
 ret_from_fork+0x2e/0x40 arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:296

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 42 Comm: kworker/0:1H Tainted: G        W          6.5.0-rc3-syzkaller-00044-g0a8db05b571a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
Workqueue: kblockd blk_mq_requeue_work
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