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SubjectRe: [PATCH 1/2] bdi: Do not use freezable workqueue
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On 10/4/19 4:00 AM, Mika Westerberg wrote:
> A removable block device, such as NVMe or SSD connected over Thunderbolt
> can be hot-removed any time including when the system is suspended. When
> device is hot-removed during suspend and the system gets resumed, kernel
> first resumes devices and then thaws the userspace including freezable
> workqueues. What happens in that case is that the NVMe driver notices
> that the device is unplugged and removes it from the system. This ends
> up calling bdi_unregister() for the gendisk which then schedules
> wb_workfn() to be run one more time.
>
> However, since the bdi_wq is still frozen flush_delayed_work() call in
> wb_shutdown() blocks forever halting system resume process. User sees
> this as hang as nothing is happening anymore.
>
> Triggering sysrq-w reveals this:
>
> Workqueue: nvme-wq nvme_remove_dead_ctrl_work [nvme]
> Call Trace:
> ? __schedule+0x2c5/0x630
> ? wait_for_completion+0xa4/0x120
> schedule+0x3e/0xc0
> schedule_timeout+0x1c9/0x320
> ? resched_curr+0x1f/0xd0
> ? wait_for_completion+0xa4/0x120
> wait_for_completion+0xc3/0x120
> ? wake_up_q+0x60/0x60
> __flush_work+0x131/0x1e0
> ? flush_workqueue_prep_pwqs+0x130/0x130
> bdi_unregister+0xb9/0x130
> del_gendisk+0x2d2/0x2e0
> nvme_ns_remove+0xed/0x110 [nvme_core]
> nvme_remove_namespaces+0x96/0xd0 [nvme_core]
> nvme_remove+0x5b/0x160 [nvme]
> pci_device_remove+0x36/0x90
> device_release_driver_internal+0xdf/0x1c0
> nvme_remove_dead_ctrl_work+0x14/0x30 [nvme]
> process_one_work+0x1c2/0x3f0
> worker_thread+0x48/0x3e0
> kthread+0x100/0x140
> ? current_work+0x30/0x30
> ? kthread_park+0x80/0x80
> ret_from_fork+0x35/0x40
>
> This is not limited to NVMes so exactly same issue can be reproduced by
> hot-removing SSD (over Thunderbolt) while the system is suspended.
>
> Prevent this from happening by removing WQ_FREEZABLE from bdi_wq.

This series looks good for me, I don't think there's a reason for
the workers to be marked freezable.

--
Jens Axboe

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