Re: [linux-pm] Is it supposed to be ok to call del_gendisk whileuserspace is frozen?

From: Alan Stern
Date: Wed Mar 03 2010 - 21:48:51 EST

On Thu, 4 Mar 2010, Rafael J. Wysocki wrote:

> > Very well. Then we still need a solution to the original problem:
> > Devices sometimes need to be unregistered during resume, but
> > del_gendisk() blocks on the writeback thread, which is frozen until
> > after the resume finishes. How do you suggest this be fixed?
> I thought about thawing the writeback thread earlier in such cases.
> Would that makes sense / is it doable at all?

My thought exactly. This is the only approach that also solves the
following race:

A driver is unloaded at the same time as a suspend starts.

The writeback thread gets frozen.

Then before the rmmod thread is frozen, it calls del_gendisk.

Delaying things by means of a workqueue (or the equivalent) might also
work, but it doesn't seem as safe. For example, some important
writebacks might end up getting delayed until too late.

Alan Stern

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