KCSAN: data-race in __bio_queue_enter / blk_mq_update_tag_set_shared

Status: moderation: reported on 2026/09/10 11:02
Subsystems: block
Labels: race:benign
[Documentation on labels]
Reported-by: syzbot+10ab08c960e5502d0e8d@syzkaller.appspotmail.com
First crash: 8h10m, last: 8h10m
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
60faef65 assessment-kcsan Benign: ✅ KCSAN: data-race in __bio_queue_enter / blk_mq_update_tag_set_shared 2026/09/10 11:01 2026/09/10 11:02 2026/09/10 11:37 1fe56c0a

Sample crash report:
==================================================================
BUG: KCSAN: data-race in __bio_queue_enter / blk_mq_update_tag_set_shared

read-write to 0xffff88810267ea34 of 4 bytes by task 6059 on cpu 1:
 __blk_mq_unfreeze_queue block/blk-mq.c:218 [inline]
 blk_mq_unfreeze_queue_nomemrestore block/blk-mq.c:232 [inline]
 blk_mq_unfreeze_queue include/linux/blk-mq.h:962 [inline]
 blk_mq_update_tag_set_shared+0xa9/0x170 block/blk-mq.c:4310
 blk_mq_add_queue_tag_set block/blk-mq.c:4341 [inline]
 blk_mq_init_allocated_queue+0x75d/0x910 block/blk-mq.c:4661
 blk_mq_alloc_queue+0xd8/0x130 block/blk-mq.c:4424
 scsi_alloc_sdev+0x3e3/0x5f0 drivers/scsi/scsi_scan.c:339
 scsi_probe_and_add_lun+0xa3/0x2030 drivers/scsi/scsi_scan.c:1228
 __scsi_scan_target+0x143/0x7f0 drivers/scsi/scsi_scan.c:1805
 scsi_scan_channel drivers/scsi/scsi_scan.c:1895 [inline]
 scsi_scan_host_selected+0x2ba/0x3f0 drivers/scsi/scsi_scan.c:1924
 scsi_scan drivers/scsi/scsi_sysfs.c:151 [inline]
 store_scan+0x371/0x3c0 drivers/scsi/scsi_sysfs.c:191
 dev_attr_store+0x4a/0x70 drivers/base/core.c:2509
 sysfs_kf_write+0xfe/0x120 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x1d2/0x2e0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57f/0x9a0 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x154e/0x2550 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810267ea34 of 4 bytes by task 3438 on cpu 0:
 __bio_queue_enter+0x1e5/0x580 block/blk-core.c:397
 bio_queue_enter block/blk.h:99 [inline]
 blk_mq_submit_bio+0x18a/0x1120 block/blk-mq.c:3127
 __submit_bio+0x54/0x3d0 block/blk-core.c:673
 __submit_bio_noacct_mq block/blk-core.c:756 [inline]
 submit_bio_noacct_nocheck+0x153/0x620 block/blk-core.c:790
 submit_bio_noacct+0x760/0x980 block/blk-core.c:925
 submit_bio+0x2a4/0x2c0 block/blk-core.c:966
 blk_crypto_submit_bio include/linux/blk-crypto.h:212 [inline]
 ext4_io_submit fs/ext4/page-io.c:396 [inline]
 io_submit_add_bh fs/ext4/page-io.c:452 [inline]
 ext4_bio_write_folio+0x702/0xa10 fs/ext4/page-io.c:547
 mpage_submit_folio fs/ext4/inode.c:2094 [inline]
 mpage_process_page_bufs+0x484/0x5e0 fs/ext4/inode.c:2201
 mpage_prepare_extent_to_map+0x83e/0xca0 fs/ext4/inode.c:2743
 ext4_do_writepages+0x70f/0x2870 fs/ext4/inode.c:2884
 ext4_writepages+0x191/0x300 fs/ext4/inode.c:3032
 do_writepages+0x1b9/0x300 mm/page-writeback.c:2560
 __writeback_single_inode+0x7b/0x790 fs/fs-writeback.c:1788
 writeback_sb_inodes+0x4d9/0xaa0 fs/fs-writeback.c:2099
 __writeback_inodes_wb+0x8a/0x180 fs/fs-writeback.c:2175
 wb_writeback+0x21e/0x510 fs/fs-writeback.c:2286
 wb_check_old_data_flush fs/fs-writeback.c:2390 [inline]
 wb_do_writeback fs/fs-writeback.c:2469 [inline]
 wb_workfn+0x740/0xa50 fs/fs-writeback.c:2497
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3479
 worker_thread+0x569/0x750 kernel/workqueue.c:3560
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000001 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3438 Comm: kworker/u8:7 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/10 11:01 upstream 50d05c7c76c9 1fe56c0a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __bio_queue_enter / blk_mq_update_tag_set_shared
* Struck through repros no longer work on HEAD.