Re: [PATCH] mhi: pci_generic: Remove WQ_MEM_RECLAIM flag from state workqueue

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Feb 24, 2021 at 11:18:50AM +0100, Loic Poulain wrote:
> A recent change created a dedicated workqueue for the state-change work
> with WQ_HIGHPRI (no strong reason for that) and WQ_MEM_RECLAIM flags,
> but the state-change work (mhi_pm_st_worker) does not guarantee forward
> progress under memory pressure, and will even wait on various memory
> allocations when e.g. creating devices, loading firmware, etc... The
> work is then not part of a memory reclaim path...
> 
> Moreover, this causes a warning in check_flush_dependency() since we end
> up in code that flushes a non-reclaim workqueue:
> 
> [   40.969601] workqueue: WQ_MEM_RECLAIM mhi_hiprio_wq:mhi_pm_st_worker [mhi] is flushing !WQ_MEM_RECLAIM events_highpri:flush_backlog
> [   40.969612] WARNING: CPU: 4 PID: 158 at kernel/workqueue.c:2607 check_flush_dependency+0x11c/0x140
> [   40.969733] Call Trace:
> [   40.969740]  __flush_work+0x97/0x1d0
> [   40.969745]  ? wake_up_process+0x15/0x20
> [   40.969749]  ? insert_work+0x70/0x80
> [   40.969750]  ? __queue_work+0x14a/0x3e0
> [   40.969753]  flush_work+0x10/0x20
> [   40.969756]  rollback_registered_many+0x1c9/0x510
> [   40.969759]  unregister_netdevice_queue+0x94/0x120
> [   40.969761]  unregister_netdev+0x1d/0x30
> [   40.969765]  mhi_net_remove+0x1a/0x40 [mhi_net]
> [   40.969770]  mhi_driver_remove+0x124/0x250 [mhi]
> [   40.969776]  device_release_driver_internal+0xf0/0x1d0
> [   40.969778]  device_release_driver+0x12/0x20
> [   40.969782]  bus_remove_device+0xe1/0x150
> [   40.969786]  device_del+0x17b/0x3e0
> [   40.969791]  mhi_destroy_device+0x9a/0x100 [mhi]
> [   40.969796]  ? mhi_unmap_single_use_bb+0x50/0x50 [mhi]
> [   40.969799]  device_for_each_child+0x5e/0xa0
> [   40.969804]  mhi_pm_st_worker+0x921/0xf50 [mhi]
> 
> Fixes: 8f7039787687 ("bus: mhi: core: Move to using high priority workqueue")
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>

Fix looks good to me but I want Bhaumik to share his review since he
authored the offending patch.

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/init.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
> index 32eb90f..03ddd6e 100644
> --- a/drivers/bus/mhi/core/init.c
> +++ b/drivers/bus/mhi/core/init.c
> @@ -890,8 +890,7 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
>  	INIT_WORK(&mhi_cntrl->st_worker, mhi_pm_st_worker);
>  	init_waitqueue_head(&mhi_cntrl->state_event);
>  
> -	mhi_cntrl->hiprio_wq = alloc_ordered_workqueue
> -				("mhi_hiprio_wq", WQ_MEM_RECLAIM | WQ_HIGHPRI);
> +	mhi_cntrl->hiprio_wq = alloc_ordered_workqueue("mhi_hiprio_wq", WQ_HIGHPRI);
>  	if (!mhi_cntrl->hiprio_wq) {
>  		dev_err(mhi_cntrl->cntrl_dev, "Failed to allocate workqueue\n");
>  		ret = -ENOMEM;
> -- 
> 2.7.4
>