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: 8f703978 ("bus: mhi: core: Move to using high priority workqueue")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/1614161930-8513-1-git-send-email-loic.poulain@linaro.orgSigned-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>