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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8881164e4438 of 8 bytes by task 32035 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:2757 [inline]
 blk_mq_flush_plug_list+0xd17/0xde0 block/blk-mq.c:2817
 __blk_flush_plug+0x216/0x290 block/blk-core.c:1190
 blk_flush_plug include/linux/blkdev.h:1006 [inline]
 io_schedule_prepare kernel/sched/core.c:9013 [inline]
 io_schedule+0x37/0x60 kernel/sched/core.c:9043
 folio_wait_bit_common+0x4c9/0x6d0 mm/filemap.c:1283
 __folio_lock+0x1e/0x30 mm/filemap.c:1621
 folio_lock include/linux/pagemap.h:1048 [inline]
 writeback_get_folio mm/page-writeback.c:2426 [inline]
 writeback_iter+0x543/0x830 mm/page-writeback.c:2520
 write_cache_pages+0xad/0x100 mm/page-writeback.c:2568
 blkdev_writepages+0x59/0x90 block/fops.c:429
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2612
 __writeback_single_inode+0x91/0x870 fs/fs-writeback.c:1650
 writeback_sb_inodes+0x4de/0xaa0 fs/fs-writeback.c:1941
 __writeback_inodes_wb+0x9a/0x1a0 fs/fs-writeback.c:2012
 wb_writeback+0x264/0x6f0 fs/fs-writeback.c:2119
 wb_check_background_flush fs/fs-writeback.c:2189 [inline]
 wb_do_writeback fs/fs-writeback.c:2277 [inline]
 wb_workfn+0x67f/0x940 fs/fs-writeback.c:2304
 process_one_work kernel/workqueue.c:3267 [inline]
 process_scheduled_works+0x465/0x990 kernel/workqueue.c:3348
 worker_thread+0x526/0x730 kernel/workqueue.c:3429
 kthread+0x1d1/0x210 kernel/kthread.c:388
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

write to 0xffff8881164e4438 of 8 bytes by task 30526 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_plug+0x4c/0x70 kernel/trace/blktrace.c:950
 trace_block_plug include/trace/events/block.h:407 [inline]
 blk_add_rq_to_plug+0x32b/0x3e0 block/blk-mq.c:1290
 blk_mq_submit_bio+0xa22/0xd90 block/blk-mq.c:3009
 __submit_bio+0x11c/0x370 block/blk-core.c:621
 __submit_bio_noacct_mq block/blk-core.c:700 [inline]
 submit_bio_noacct_nocheck+0x533/0x6d0 block/blk-core.c:729
 submit_bio_noacct+0x681/0x830 block/blk-core.c:839
 submit_bio+0x218/0x230 block/blk-core.c:881
 submit_bh_wbc+0x2de/0x320 fs/buffer.c:2804
 __block_write_full_folio+0x577/0x8d0 fs/buffer.c:1892
 block_write_full_folio+0x293/0x2b0
 write_cache_pages+0x62/0x100 mm/page-writeback.c:2569
 blkdev_writepages+0x59/0x90 block/fops.c:429
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2612
 filemap_fdatawrite_wbc+0xdb/0x100 mm/filemap.c:397
 __filemap_fdatawrite_range mm/filemap.c:430 [inline]
 __filemap_fdatawrite mm/filemap.c:436 [inline]
 filemap_flush+0x61/0x90 mm/filemap.c:463
 sync_blockdev_nowait+0x36/0x50 block/bdev.c:195
 sync_filesystem+0xe3/0x190 fs/sync.c:60
 generic_shutdown_super+0x42/0x210 fs/super.c:620
 kill_block_super+0x2a/0x70 fs/super.c:1675
 deactivate_locked_super+0x7d/0x1c0 fs/super.c:472
 deactivate_super+0x9f/0xb0 fs/super.c:505
 cleanup_mnt+0x272/0x2e0 fs/namespace.c:1267
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1274
 task_work_run+0x13a/0x1a0 kernel/task_work.c:180
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218
 do_syscall_64+0xda/0x1d0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30526 Comm: syz-executor.3 Tainted: G        W          6.9.0-rc6-syzkaller-00290-gb9158815de52 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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