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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff888140949238 of 8 bytes by task 1391 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_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:2752 [inline]
 blk_mq_flush_plug_list+0xd4c/0xe00 block/blk-mq.c:2817
 __blk_flush_plug+0x210/0x260 block/blk-core.c:1142
 blk_finish_plug+0x47/0x60 block/blk-core.c:1166
 ext4_do_writepages+0x1bc7/0x2100 fs/ext4/inode.c:2726
 ext4_writepages+0x15e/0x2e0 fs/ext4/inode.c:2764
 do_writepages+0x1c2/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:390
 __filemap_fdatawrite_range mm/filemap.c:423 [inline]
 filemap_write_and_wait_range+0xe0/0x210 mm/filemap.c:678
 kiocb_write_and_wait+0x79/0x110 mm/filemap.c:2738
 __iomap_dio_rw+0x512/0x1080 fs/iomap/direct-io.c:592
 iomap_dio_rw+0x40/0x90 fs/iomap/direct-io.c:748
 ext4_dio_read_iter fs/ext4/file.c:94 [inline]
 ext4_file_read_iter+0x21c/0x2a0 fs/ext4/file.c:145
 call_read_iter include/linux/fs.h:1979 [inline]
 copy_splice_read+0x26b/0x4b0 fs/splice.c:364
 vfs_splice_read fs/splice.c:992 [inline]
 splice_direct_to_actor+0x2aa/0x690 fs/splice.c:1069
 do_splice_direct+0x10d/0x190 fs/splice.c:1194
 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 0xffff888140949238 of 8 bytes by task 1381 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:407 [inline]
 blk_add_rq_to_plug+0x2b4/0x3e0 block/blk-mq.c:1295
 blk_mq_submit_bio+0x692/0xd70 block/blk-mq.c:3012
 __submit_bio+0x11c/0x350 block/blk-core.c:599
 __submit_bio_noacct_mq block/blk-core.c:678 [inline]
 submit_bio_noacct_nocheck+0x4ad/0x5e0 block/blk-core.c:707
 submit_bio_noacct+0x700/0x8a0 block/blk-core.c:801
 submit_bio+0xb7/0xc0 block/blk-core.c:834
 ext4_io_submit+0x8a/0xa0 fs/ext4/page-io.c:378
 ext4_do_writepages+0xb3a/0x2100 fs/ext4/inode.c:2695
 ext4_writepages+0x15e/0x2e0 fs/ext4/inode.c:2764
 do_writepages+0x1c2/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:390
 __filemap_fdatawrite_range mm/filemap.c:423 [inline]
 filemap_write_and_wait_range+0xe0/0x210 mm/filemap.c:678
 ext4_punch_hole+0xc5/0x7c0 fs/ext4/inode.c:3910
 ext4_fallocate+0x209/0x1190 fs/ext4/extents.c:4706
 vfs_fallocate+0x378/0x3e0 fs/open.c:324
 madvise_remove mm/madvise.c:1011 [inline]
 madvise_vma_behavior mm/madvise.c:1035 [inline]
 madvise_walk_vmas mm/madvise.c:1270 [inline]
 do_madvise+0x7a9/0x2970 mm/madvise.c:1450
 __do_sys_madvise mm/madvise.c:1463 [inline]
 __se_sys_madvise mm/madvise.c:1461 [inline]
 __x64_sys_madvise+0x60/0x70 mm/madvise.c:1461
 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: 1381 Comm: syz-executor.5 Not tainted 6.6.0-rc1-syzkaller-00240-gf0b0d403eabb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
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