INFO: task hung in mmc_stop_host

Status: upstream: reported on 2026/09/05 04:28
Reported-by: syzbot+54c875491fbcfa7e2830@syzkaller.appspotmail.com
First crash: 45d, last: 24d
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in mmc_stop_host prio:high mmc 1 1089 32m 56d 0/29 upstream: reported on 2026/08/25 00:03
linux-6.1 INFO: task hung in mmc_stop_host 1 2 45d 50d 0/3 upstream: reported on 2026/08/30 19:05
linux-6.6 INFO: task hung in mmc_stop_host 1 5 5d02h 66d 0/2 upstream: reported on 2026/08/14 22:00

Sample crash report:
INFO: task kworker/0:1:13 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:1     state:D
 stack:16112 pid:   13 ppid:     2 flags:0x00004000
Workqueue: usb_hub_wq hub_event
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0xbd/0x2d0 kernel/time/timer.c:2093
 do_wait_for_common+0x295/0x460 kernel/sched/completion.c:85
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x48/0x60 kernel/sched/completion.c:138
 __flush_work+0x15a/0x210 kernel/workqueue.c:3094
 __cancel_work_timer+0x3f4/0x560 kernel/workqueue.c:3181
 __mmc_stop_host drivers/mmc/core/core.c:2294 [inline]
 mmc_stop_host+0xd5/0x460 drivers/mmc/core/core.c:2299
 mmc_remove_host+0x11/0x60 drivers/mmc/core/host.c:642
 vub300_disconnect+0x14b/0x2e0 drivers/mmc/host/vub300.c:2388
 usb_unbind_interface+0x203/0x870 drivers/usb/core/driver.c:458
 __device_release_driver drivers/base/dd.c:1249 [inline]
 device_release_driver_internal+0x487/0x710 drivers/base/dd.c:1282
 bus_remove_device+0x2dd/0x400 drivers/base/bus.c:531
 device_del+0x63f/0xa80 drivers/base/core.c:3615
 usb_disable_device+0x3e7/0x8a0 drivers/usb/core/message.c:1472
 usb_disconnect+0x33c/0x8a0 drivers/usb/core/hub.c:2292
 hub_port_connect drivers/usb/core/hub.c:5346 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5642 [inline]
 port_event drivers/usb/core/hub.c:5804 [inline]
 hub_event+0x1d64/0x5260 drivers/usb/core/hub.c:5886
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
INFO: task kworker/0:6:4758 blocked for more than 148 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:6     state:D
 stack:25264 pid: 4758 ppid:     2 flags:0x00004000
Workqueue: events_freezable mmc_rescan

Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0xbd/0x2d0 kernel/time/timer.c:2093
 do_wait_for_common+0x295/0x460 kernel/sched/completion.c:85
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x48/0x60 kernel/sched/completion.c:138
 mmc_wait_for_req_done+0x33/0x460 drivers/mmc/core/core.c:403
 mmc_wait_for_cmd+0x174/0x280 drivers/mmc/core/core.c:639
 mmc_io_rw_direct_host drivers/mmc/core/sdio_ops.c:83 [inline]
 sdio_reset+0x20e/0x3b0 drivers/mmc/core/sdio_ops.c:215
 mmc_rescan_try_freq drivers/mmc/core/core.c:2073 [inline]
 mmc_rescan+0x65f/0xe30 drivers/mmc/core/core.c:2256
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Showing all locks held in the system:
5 locks held by kworker/0:1/13:
 #0: ffff88801bf42d38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x75c/0xff0 kernel/workqueue.c:-1
 #1: ffffc90000d27d00 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x79e/0xff0 kernel/workqueue.c:2285
 #2: ffff888148741220 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:809 [inline]
 #2: ffff888148741220 (&dev->mutex){....}-{3:3}, at: hub_event+0x178/0x5260 drivers/usb/core/hub.c:5832
 #3: ffff888024ae3220 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:809 [inline]
 #3: ffff888024ae3220 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0xf8/0x8a0 drivers/usb/core/hub.c:2283
 #4: ffff88806293e1a8 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:809 [inline]
 #4: ffff88806293e1a8 (&dev->mutex){....}-{3:3}, at: __device_driver_lock drivers/base/dd.c:1064 [inline]
 #4: ffff88806293e1a8 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0xa1/0x710 drivers/base/dd.c:1279
1 lock held by khungtaskd/27:
 #0: ffffffff8c31ef60 (rcu_read_lock
){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
4 locks held by udevd/3557:
2 locks held by getty/3945:
 #0: ffff88814d919098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
 #1: ffffc90002d032e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x594/0x1a50 drivers/tty/n_tty.c:2158
2 locks held by kworker/0:6/4758:
 #0: ffff888016c71538 ((wq_completion)events_freezable){+.+.}-{0:0}, at: process_one_work+0x75c/0xff0 kernel/workqueue.c:-1
 #1: ffffc9000337fd00 ((work_completion)(&(&host->detect)->work)){+.+.}-{0:0}, at: process_one_work+0x79e/0xff0 kernel/workqueue.c:2285
2 locks held by udevd/7018:
 #0: 
ffff888020716118 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf1/0x780 block/bdev.c:911
 #1: ffff8881479c0468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xa9/0xb50 drivers/block/loop.c:1366

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 27 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
 watchdog+0xe1b/0xe60 kernel/hung_task.c:369
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 14 Comm: ksoftirqd/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:kasan_record_aux_stack+0x0/0x100 mm/kasan/generic.c:332
Code: 00 00 e9 43 0c 51 02 0f 1f 00 48 89 f2 be f5 00 00 00 e9 33 0c 51 02 0f 1f 00 48 89 f2 be f8 00 00 00 e9 23 0c 51 02 0f 1f 00 <41> 56 53 48 89 fb e8 45 ec ff ff 48 85 c0 0f 84 a7 00 00 00 48 89
RSP: 0018:ffffc90000d37948 EFLAGS: 00000046
RAX: ffff888016c79800 RBX: dffffc0000000000 RCX: ffff88813fe29dc0
RDX: 0000000000000100 RSI: ffff88807eb9d720 RDI: ffff88807eb9d720
RBP: 0000000000000002 R08: ffffffff96512903 R09: 1ffffffff2ca2520
R10: dffffc0000000000 R11: fffffbfff2ca2521 R12: dffffc0000000000
R13: 0000000000000001 R14: ffff88802bdb4400 R15: ffff88807eb9d720
FS:  0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3992756000 CR3: 000000002aa7c000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 insert_work+0x54/0x3d0 kernel/workqueue.c:1366
 __queue_work+0x90b/0xc80 kernel/workqueue.c:1532
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1694 [inline]
 __run_timers+0x598/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 run_ksoftirqd+0xa4/0x100 kernel/softirq.c:943
 smpboot_thread_fn+0x520/0x990 kernel/smpboot.c:164
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/26 07:55 linux-5.15.y 0248c33e835e a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in mmc_stop_host
2026/09/05 04:27 linux-5.15.y 0996e0926f6b 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in mmc_stop_host
* Struck through repros no longer work on HEAD.