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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff888135b85838 of 8 bytes by task 9633 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_bio kernel/trace/blktrace.c:903 [inline]
 blk_add_trace_bio_queue+0x130/0x140 kernel/trace/blktrace.c:935
 trace_block_bio_queue include/trace/events/block.h:383 [inline]
 submit_bio_noacct_nocheck+0x66b/0x6d0 block/blk-core.c:710
 submit_bio_noacct+0x681/0x830 block/blk-core.c:837
 submit_bio+0x218/0x230 block/blk-core.c:879
 swap_writepage_bdev_async mm/page_io.c:371 [inline]
 __swap_writepage+0x612/0xc50 mm/page_io.c:389
 swap_writepage+0xa9/0x160 mm/page_io.c:209
 pageout mm/vmscan.c:660 [inline]
 shrink_folio_list+0x1858/0x2460 mm/vmscan.c:1323
 reclaim_folio_list+0x81/0x1e0 mm/vmscan.c:2108
 reclaim_pages+0x227/0x290 mm/vmscan.c:2145
 madvise_cold_or_pageout_pte_range+0xaa0/0xb30 mm/madvise.c:527
 walk_pmd_range mm/pagewalk.c:143 [inline]
 walk_pud_range mm/pagewalk.c:221 [inline]
 walk_p4d_range mm/pagewalk.c:256 [inline]
 walk_pgd_range+0x80d/0xef0 mm/pagewalk.c:293
 __walk_page_range+0xc5/0x330 mm/pagewalk.c:395
 walk_page_range+0x2c5/0x400 mm/pagewalk.c:521
 madvise_pageout_page_range mm/madvise.c:586 [inline]
 madvise_pageout mm/madvise.c:613 [inline]
 madvise_vma_behavior mm/madvise.c:1032 [inline]
 madvise_walk_vmas mm/madvise.c:1261 [inline]
 do_madvise+0x1a38/0x2620 mm/madvise.c:1441
 __do_sys_madvise mm/madvise.c:1454 [inline]
 __se_sys_madvise mm/madvise.c:1452 [inline]
 __x64_sys_madvise+0x61/0x70 mm/madvise.c:1452
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

write to 0xffff888135b85838 of 8 bytes by task 9640 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_bio kernel/trace/blktrace.c:903 [inline]
 blk_add_trace_bio_backmerge+0x130/0x140 kernel/trace/blktrace.c:923
 trace_block_bio_backmerge include/trace/events/block.h:361 [inline]
 bio_attempt_back_merge+0x4b3/0x510 block/blk-merge.c:989
 blk_attempt_bio_merge+0x44f/0x490 block/blk-merge.c:1072
 blk_attempt_plug_merge+0xb5/0x100 block/blk-merge.c:1119
 blk_mq_attempt_bio_merge block/blk-mq.c:2863 [inline]
 blk_mq_submit_bio+0x597/0xd90 block/blk-mq.c:2985
 __submit_bio+0x11c/0x370 block/blk-core.c:619
 __submit_bio_noacct_mq block/blk-core.c:698 [inline]
 submit_bio_noacct_nocheck+0x533/0x6d0 block/blk-core.c:727
 submit_bio_noacct+0x681/0x830 block/blk-core.c:837
 submit_bio+0x218/0x230 block/blk-core.c:879
 swap_writepage_bdev_async mm/page_io.c:371 [inline]
 __swap_writepage+0x612/0xc50 mm/page_io.c:389
 swap_writepage+0xa9/0x160 mm/page_io.c:209
 pageout mm/vmscan.c:660 [inline]
 shrink_folio_list+0x1858/0x2460 mm/vmscan.c:1323
 reclaim_folio_list+0x81/0x1e0 mm/vmscan.c:2108
 reclaim_pages+0x227/0x290 mm/vmscan.c:2145
 madvise_cold_or_pageout_pte_range+0xaa0/0xb30 mm/madvise.c:527
 walk_pmd_range mm/pagewalk.c:143 [inline]
 walk_pud_range mm/pagewalk.c:221 [inline]
 walk_p4d_range mm/pagewalk.c:256 [inline]
 walk_pgd_range+0x80d/0xef0 mm/pagewalk.c:293
 __walk_page_range+0xc5/0x330 mm/pagewalk.c:395
 walk_page_range+0x2c5/0x400 mm/pagewalk.c:521
 madvise_pageout_page_range mm/madvise.c:586 [inline]
 madvise_pageout mm/madvise.c:613 [inline]
 madvise_vma_behavior mm/madvise.c:1032 [inline]
 madvise_walk_vmas mm/madvise.c:1261 [inline]
 do_madvise+0x1a38/0x2620 mm/madvise.c:1441
 __do_sys_madvise mm/madvise.c:1454 [inline]
 __se_sys_madvise mm/madvise.c:1452 [inline]
 __x64_sys_madvise+0x61/0x70 mm/madvise.c:1452
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

value changed: 0x0000000000000040 -> 0x0000000000000030

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9640 Comm: syz-executor.2 Not tainted 6.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
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syz-executor.2 (9640) used greatest stack depth: 9128 bytes left