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BUG: KCSAN: data-race in relay_switch_subbuf / relay_switch_subbuf

write to 0xffff888112e6ae38 of 8 bytes by task 2745 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_unplug+0x76/0xb0 kernel/trace/blktrace.c:969
 trace_block_unplug include/trace/events/block.h:452 [inline]
 blk_mq_dispatch_plug_list block/blk-mq.c:2739 [inline]
 blk_mq_flush_plug_list+0xd17/0xde0 block/blk-mq.c:2799
 __blk_flush_plug+0x216/0x290 block/blk-core.c:1194
 blk_finish_plug+0x48/0x70 block/blk-core.c:1221
 jbd2_journal_commit_transaction+0x1bc5/0x33e0 fs/jbd2/commit.c:794
 kjournald2+0x243/0x430 fs/jbd2/journal.c:201
 kthread+0x1d1/0x210 kernel/kthread.c:389
 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 0xffff888112e6ae38 of 8 bytes by task 7848 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:969
 trace_block_unplug include/trace/events/block.h:452 [inline]
 blk_mq_dispatch_plug_list block/blk-mq.c:2739 [inline]
 blk_mq_flush_plug_list+0xd17/0xde0 block/blk-mq.c:2799
 __blk_flush_plug+0x216/0x290 block/blk-core.c:1194
 blk_finish_plug+0x48/0x70 block/blk-core.c:1221
 ext4_do_writepages+0x1bd0/0x2110 fs/ext4/inode.c:2730
 ext4_writepages+0x159/0x2e0 fs/ext4/inode.c:2768
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2634
 filemap_fdatawrite_wbc+0xdb/0x100 mm/filemap.c:397
 __filemap_fdatawrite_range mm/filemap.c:430 [inline]
 file_write_and_wait_range+0xc8/0x170 mm/filemap.c:788
 ext4_sync_file+0x134/0x6c0 fs/ext4/fsync.c:158
 vfs_fsync_range+0x122/0x140 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2794 [inline]
 ext4_buffered_write_iter+0x338/0x380 fs/ext4/file.c:305
 ext4_file_write_iter+0x29f/0xe30
 __kernel_write_iter+0x24f/0x4d0 fs/read_write.c:523
 dump_emit_page fs/coredump.c:893 [inline]
 dump_user_range+0x3a7/0x550 fs/coredump.c:954
 elf_core_dump+0x1aeb/0x1c30 fs/binfmt_elf.c:2083
 do_coredump+0xff6/0x1860 fs/coredump.c:767
 get_signal+0xdc1/0x1080 kernel/signal.c:2894
 arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 irqentry_exit_to_user_mode+0x94/0x130 kernel/entry/common.c:231
 irqentry_exit+0x12/0x50 kernel/entry/common.c:334
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623

value changed: 0x0000000000000030 -> 0x0000000000000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7848 Comm: syz.4.1357 Not tainted 6.10.0-rc5-syzkaller-00253-gde0a9f448633 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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