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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff8881100dce38 of 8 bytes by interrupt 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_rq kernel/trace/blktrace.c:844 [inline]
 blk_add_trace_rq_complete+0x1b7/0x1c0 kernel/trace/blktrace.c:876
 trace_block_rq_complete include/trace/events/block.h:149 [inline]
 blk_update_request+0x8f8/0x950 block/blk-mq.c:894
 scsi_end_request+0x52/0x4f0 drivers/scsi/scsi_lib.c:631
 scsi_io_completion+0x9f/0x200 drivers/scsi/scsi_lib.c:1069
 scsi_finish_command+0x1be/0x1d0 drivers/scsi/scsi.c:198
 scsi_complete+0x19a/0x1d0 drivers/scsi/scsi_lib.c:1531
 blk_complete_reqs block/blk-mq.c:1129 [inline]
 blk_done_softirq+0x74/0xb0 block/blk-mq.c:1134
 __do_softirq+0xc8/0x285 kernel/softirq.c:554
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu kernel/softirq.c:633 [inline]
 irq_exit_rcu+0x3c/0x90 kernel/softirq.c:645
 common_interrupt+0x81/0x90 arch/x86/kernel/irq.c:247
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:693
 kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
 EXT4_SB fs/ext4/ext4.h:1760 [inline]
 ext4_get_group_desc+0x5e/0x190 fs/ext4/balloc.c:273
 __ext4_get_inode_loc+0x112/0x8f0 fs/ext4/inode.c:4348
 ext4_get_inode_loc fs/ext4/inode.c:4497 [inline]
 ext4_reserve_inode_write+0xb0/0x200 fs/ext4/inode.c:5728
 __ext4_mark_inode_dirty+0x8e/0x440 fs/ext4/inode.c:5905
 __ext4_new_inode+0x20e2/0x2270 fs/ext4/ialloc.c:1344
 ext4_symlink+0x242/0x5a0 fs/ext4/namei.c:3395
 vfs_symlink+0xca/0x1b0 fs/namei.c:4484
 do_symlinkat+0xe3/0x350 fs/namei.c:4510
 __do_sys_symlinkat fs/namei.c:4526 [inline]
 __se_sys_symlinkat fs/namei.c:4523 [inline]
 __x64_sys_symlinkat+0x62/0x70 fs/namei.c:4523
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

write to 0xffff8881100dce38 of 8 bytes by task 26174 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+0x72/0x7a

value changed: 0x0000000000000040 -> 0x0000000000000030

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26174 Comm: syz-executor.2 Not tainted 6.9.0-rc1-syzkaller-00206-g4535e1a4174c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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