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

write to 0xffff88813a93e638 of 8 bytes by task 22898 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_unplug+0x76/0xb0 kernel/trace/blktrace.c:970
 trace_block_unplug include/trace/events/block.h:452 [inline]
 blk_mq_dispatch_plug_list block/blk-mq.c:2753 [inline]
 blk_mq_flush_plug_list+0xcfa/0xdb0 block/blk-mq.c:2813
 __blk_flush_plug+0x210/0x260 block/blk-core.c:1166
 blk_finish_plug+0x47/0x60 block/blk-core.c:1190
 read_pages+0x4bf/0x530 mm/readahead.c:183
 page_cache_ra_unbounded+0x2aa/0x2e0 mm/readahead.c:269
 do_page_cache_ra mm/readahead.c:299 [inline]
 page_cache_ra_order mm/readahead.c:544 [inline]
 ondemand_readahead+0x524/0x690 mm/readahead.c:666
 page_cache_sync_ra+0x27e/0x2a0 mm/readahead.c:693
 page_cache_sync_readahead include/linux/pagemap.h:1300 [inline]
 filemap_get_pages+0x251/0xf90 mm/filemap.c:2498
 filemap_splice_read+0x238/0x7f0 mm/filemap.c:2870
 ext4_file_splice_read+0x95/0xb0 fs/ext4/file.c:158
 do_splice_read fs/splice.c:985 [inline]
 splice_direct_to_actor+0x268/0x650 fs/splice.c:1089
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x960 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

write to 0xffff88813a93e638 of 8 bytes by task 22892 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:407 [inline]
 blk_add_rq_to_plug+0x327/0x3d0 block/blk-mq.c:1291
 blk_mq_submit_bio+0x61d/0xdb0 block/blk-mq.c:3009
 __submit_bio+0x11c/0x350 block/blk-core.c:607
 __submit_bio_noacct_mq block/blk-core.c:686 [inline]
 submit_bio_noacct_nocheck+0x449/0x5e0 block/blk-core.c:715
 submit_bio_noacct+0x67d/0x830 block/blk-core.c:825
 submit_bio+0xb7/0xc0 block/blk-core.c:858
 iomap_dio_submit_bio fs/iomap/direct-io.c:80 [inline]
 iomap_dio_bio_iter+0xa4a/0xbe0 fs/iomap/direct-io.c:417
 __iomap_dio_rw+0x8db/0x1090 fs/iomap/direct-io.c:659
 iomap_dio_rw+0x40/0x90 fs/iomap/direct-io.c:748
 ext4_dio_write_iter fs/ext4/file.c:577 [inline]
 ext4_file_write_iter+0xa8a/0xe10 fs/ext4/file.c:696
 call_write_iter include/linux/fs.h:2085 [inline]
 iter_file_splice_write+0x4e0/0x840 fs/splice.c:743
 do_splice_from fs/splice.c:941 [inline]
 direct_splice_actor+0x167/0x2c0 fs/splice.c:1164
 splice_direct_to_actor+0x2fb/0x650 fs/splice.c:1108
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x960 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22892 Comm: syz-executor.4 Not tainted 6.7.0-syzkaller-11889-g86c4d58a99ab #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
==================================================================
syz-executor.4 (22892) used greatest stack depth: 9928 bytes left