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

write to 0xffff888135dcd838 of 8 bytes by task 6183 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_mpage_readpages+0xff5/0x1050 fs/ext4/readpage.c:398
 ext4_readahead+0x97/0xa0 fs/ext4/inode.c:3104
 read_pages+0xa6/0x560 mm/readahead.c:160
 page_cache_ra_unbounded+0x2a9/0x2e0 mm/readahead.c:269
 do_page_cache_ra mm/readahead.c:299 [inline]
 page_cache_ra_order mm/readahead.c:559 [inline]
 ondemand_readahead+0x550/0x6c0 mm/readahead.c:681
 page_cache_sync_ra+0x284/0x2a0 mm/readahead.c:708
 page_cache_sync_readahead include/linux/pagemap.h:1213 [inline]
 filemap_get_pages+0x254/0xea0 mm/filemap.c:2563
 filemap_splice_read+0x23a/0x810 mm/filemap.c:2925
 ext4_file_splice_read+0x95/0xb0 fs/ext4/file.c:158
 vfs_splice_read fs/splice.c:994 [inline]
 splice_direct_to_actor+0x28c/0x690 fs/splice.c:1070
 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 0xffff888135dcd838 of 8 bytes by task 6194 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_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_mpage_readpages+0xff5/0x1050 fs/ext4/readpage.c:398
 ext4_readahead+0x97/0xa0 fs/ext4/inode.c:3104
 read_pages+0xa6/0x560 mm/readahead.c:160
 page_cache_ra_unbounded+0x2a9/0x2e0 mm/readahead.c:269
 do_page_cache_ra mm/readahead.c:299 [inline]
 page_cache_ra_order mm/readahead.c:559 [inline]
 ondemand_readahead+0x550/0x6c0 mm/readahead.c:681
 page_cache_sync_ra+0x284/0x2a0 mm/readahead.c:708
 page_cache_sync_readahead include/linux/pagemap.h:1213 [inline]
 filemap_get_pages+0x254/0xea0 mm/filemap.c:2563
 filemap_splice_read+0x23a/0x810 mm/filemap.c:2925
 ext4_file_splice_read+0x95/0xb0 fs/ext4/file.c:158
 vfs_splice_read fs/splice.c:994 [inline]
 splice_direct_to_actor+0x28c/0x690 fs/splice.c:1070
 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

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6194 Comm: syz-executor.4 Not tainted 6.5.0-rc3-syzkaller-00025-g5f0bc0b042fc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
==================================================================
syz-executor.4 (6194) used greatest stack depth: 9576 bytes left