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

write to 0xffff888140bdfe38 of 8 bytes by task 6323 on cpu 1:
 relay_switch_subbuf+0x39e/0x3b0 kernel/relay.c:708
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x66a/0x730 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:2762 [inline]
 blk_mq_flush_plug_list+0xd17/0xde0 block/blk-mq.c:2822
 __blk_flush_plug+0x216/0x280 block/blk-core.c:1188
 blk_finish_plug+0x48/0x70 block/blk-core.c:1214
 ext4_do_writepages+0x1bc9/0x2100 fs/ext4/inode.c:2730
 ext4_writepages+0x15f/0x2f0 fs/ext4/inode.c:2768
 do_writepages+0x1c6/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0x100 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 file_write_and_wait_range+0xf4/0x190 mm/filemap.c:779
 ext4_sync_file+0x134/0x6c0 fs/ext4/fsync.c:158
 vfs_fsync_range+0x122/0x140 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2793 [inline]
 ext4_buffered_write_iter+0x338/0x380 fs/ext4/file.c:305
 ext4_file_write_iter+0x29f/0xe30
 call_write_iter include/linux/fs.h:2108 [inline]
 iter_file_splice_write+0x5e6/0x970 fs/splice.c:743
 do_splice_from fs/splice.c:941 [inline]
 direct_splice_actor+0x16c/0x2c0 fs/splice.c:1164
 splice_direct_to_actor+0x305/0x670 fs/splice.c:1108
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x970 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1356 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0xbd/0x150 fs/read_write.c:1348
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

write to 0xffff888140bdfe38 of 8 bytes by task 6318 on cpu 0:
 relay_switch_subbuf+0x39e/0x3b0 kernel/relay.c:708
 relay_reserve include/linux/relay.h:248 [inline]
 __blk_add_trace+0x66a/0x730 kernel/trace/blktrace.c:276
 blk_add_trace_rq kernel/trace/blktrace.c:844 [inline]
 blk_add_trace_rq_issue+0x1ba/0x1d0 kernel/trace/blktrace.c:857
 trace_block_rq_issue include/trace/events/block.h:229 [inline]
 blk_mq_start_request+0x327/0x380 block/blk-mq.c:1253
 scsi_queue_rq+0x14be/0x1a20 drivers/scsi/scsi_lib.c:1759
 blk_mq_dispatch_rq_list+0x2ef/0x10d0 block/blk-mq.c:2058
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:170 [inline]
 blk_mq_do_dispatch_sched block/blk-mq-sched.c:184 [inline]
 __blk_mq_sched_dispatch_requests+0x604/0xd50 block/blk-mq-sched.c:309
 blk_mq_sched_dispatch_requests+0x78/0xe0 block/blk-mq-sched.c:331
 blk_mq_run_hw_queue+0x29c/0x4d0 block/blk-mq.c:2273
 blk_mq_flush_plug_list+0x7bc/0xde0 block/blk-mq.c:2822
 __blk_flush_plug+0x216/0x280 block/blk-core.c:1188
 blk_finish_plug+0x48/0x70 block/blk-core.c:1214
 ext4_do_writepages+0x1bc9/0x2100 fs/ext4/inode.c:2730
 ext4_writepages+0x15f/0x2f0 fs/ext4/inode.c:2768
 do_writepages+0x1c6/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0x100 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 file_write_and_wait_range+0xf4/0x190 mm/filemap.c:779
 ext4_sync_file+0x134/0x6c0 fs/ext4/fsync.c:158
 vfs_fsync_range+0x122/0x140 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2793 [inline]
 ext4_buffered_write_iter+0x338/0x380 fs/ext4/file.c:305
 ext4_file_write_iter+0x29f/0xe30
 call_write_iter include/linux/fs.h:2108 [inline]
 iter_file_splice_write+0x5e6/0x970 fs/splice.c:743
 do_splice_from fs/splice.c:941 [inline]
 direct_splice_actor+0x16c/0x2c0 fs/splice.c:1164
 splice_direct_to_actor+0x305/0x670 fs/splice.c:1108
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x970 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1356 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0xbd/0x150 fs/read_write.c:1348
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6318 Comm: syz-executor.2 Not tainted 6.8.0-syzkaller-05562-g61387b8dcf1d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
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syz-executor.2 (6318) used greatest stack depth: 8824 bytes left