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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8881454a1a38 of 8 bytes by task 24576 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_remap+0x165/0x180 kernel/trace/blktrace.c:1021
 trace_block_bio_remap include/trace/events/block.h:507 [inline]
 blk_partition_remap block/blk-core.c:571 [inline]
 submit_bio_noacct+0x7dd/0x830 block/blk-core.c:762
 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:654 [inline]
 shrink_folio_list+0x1977/0x2580 mm/vmscan.c:1316
 reclaim_folio_list+0x7b/0x1e0 mm/vmscan.c:2101
 reclaim_pages+0x221/0x280 mm/vmscan.c:2137
 madvise_cold_or_pageout_pte_range+0xa8a/0xb20 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+0x80c/0xed0 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 0xffff8881454a1a38 of 8 bytes by task 24587 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_remap+0x165/0x180 kernel/trace/blktrace.c:1021
 trace_block_bio_remap include/trace/events/block.h:507 [inline]
 blk_partition_remap block/blk-core.c:571 [inline]
 submit_bio_noacct+0x7dd/0x830 block/blk-core.c:762
 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:654 [inline]
 shrink_folio_list+0x1977/0x2580 mm/vmscan.c:1316
 reclaim_folio_list+0x7b/0x1e0 mm/vmscan.c:2101
 reclaim_pages+0x221/0x280 mm/vmscan.c:2137
 madvise_cold_or_pageout_pte_range+0xa8a/0xb20 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+0x80c/0xed0 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: 0x0000000000000030 -> 0x0000000000000040

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24587 Comm: syz-executor.0 Tainted: G        W          6.8.0-syzkaller-08073-g480e035fc4c7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
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