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

write to 0xffff88810a44d638 of 8 bytes by task 23660 on cpu 1:
 relay_switch_subbuf+0x336/0x340 kernel/relay.c:796
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x6db/0x7a0 kernel/trace/blktrace.c:274
 blk_add_trace_bio_remap+0x1d1/0x1e0 kernel/trace/blktrace.c:1070
 trace_block_bio_remap include/trace/events/block.h:573 [inline]
 blk_partition_remap+0x456/0x4a0 block/blk-core.c:761
 submit_bio_checks+0x1f9/0xb20 block/blk-core.c:829
 submit_bio_noacct+0x33/0x930 block/blk-core.c:1044
 submit_bio+0x1f3/0x360 block/blk-core.c:1129
 submit_bh_wbc+0x38c/0x3d0 fs/buffer.c:3054
 submit_bh fs/buffer.c:3060 [inline]
 __sync_dirty_buffer+0x12c/0x1d0 fs/buffer.c:3155
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3168
 ext4_write_inode+0x28b/0x390 fs/ext4/inode.c:5227
 write_inode+0x8c/0x1f0 fs/fs-writeback.c:1320
 __writeback_single_inode+0x304/0x560 fs/fs-writeback.c:1516
 writeback_single_inode+0x126/0x580 fs/fs-writeback.c:1570
 sync_inode fs/fs-writeback.c:2606 [inline]
 sync_inode_metadata+0x52/0x70 fs/fs-writeback.c:2626
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x327/0x6a0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2723 [inline]
 ext4_buffered_write_iter+0x384/0x3d0 fs/ext4/file.c:278
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1887 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x574/0xb70 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88810a44d638 of 8 bytes by task 23659 on cpu 0:
 relay_switch_subbuf+0x336/0x340 kernel/relay.c:796
 relay_reserve include/linux/relay.h:261 [inline]
 __blk_add_trace+0x6db/0x7a0 kernel/trace/blktrace.c:274
 blk_add_trace_bio_remap+0x1d1/0x1e0 kernel/trace/blktrace.c:1070
 trace_block_bio_remap include/trace/events/block.h:573 [inline]
 blk_partition_remap+0x456/0x4a0 block/blk-core.c:761
 submit_bio_checks+0x1f9/0xb20 block/blk-core.c:829
 submit_bio_noacct+0x33/0x930 block/blk-core.c:1044
 submit_bio+0x1f3/0x360 block/blk-core.c:1129
 submit_bh_wbc+0x38c/0x3d0 fs/buffer.c:3054
 submit_bh fs/buffer.c:3060 [inline]
 __sync_dirty_buffer+0x12c/0x1d0 fs/buffer.c:3155
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3168
 ext4_write_inode+0x28b/0x390 fs/ext4/inode.c:5227
 write_inode+0x8c/0x1f0 fs/fs-writeback.c:1320
 __writeback_single_inode+0x304/0x560 fs/fs-writeback.c:1516
 writeback_single_inode+0x126/0x580 fs/fs-writeback.c:1570
 sync_inode fs/fs-writeback.c:2606 [inline]
 sync_inode_metadata+0x52/0x70 fs/fs-writeback.c:2626
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x327/0x6a0 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2723 [inline]
 ext4_buffered_write_iter+0x384/0x3d0 fs/ext4/file.c:278
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1887 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x574/0xb70 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23659 Comm: syz-executor.1 Not tainted 5.10.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================