removing refrigerator does not help with s2ram vs. fuse deadlocks (was Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway)

Pavel Machek
2007-07-05T09:15:35Z

Hi!

> > The fact remains that lots of drivers would still need to be changed.
> > In the read and write methods someone would have to add code amounting
> > to this:
> >
> > if (suspend_is_under_way()) {
> > mutex_unlock(...);
> > block_until_resume();
> > goto restart;
> > }
> >
> > Freezing userspace is a small amount of code by comparison.
>
> Normally devices have some sort of queue of pending operations. So
> all that is required on suspend is to stop processing the queue and
> wait for any currently-underway operations to complete. The blocking
> then happens naturally using the normal I/O wait mechanisms.

So... instead of one big freezer (we know it is problematic), you have
100 small freezers, problematic in same way :-(.

Let's take current FUSE problems, and see if they have problem on PPC,
ok?

Let's say FUSE thread touches one of those "blocking" devices. It is
now in D state, somewhere in kernel.... exactly same way refrigerator
works.

Now, if kernel needs FUSE services for some reason (that's the problem
we hit in s2ram case, right?), we have a deadlock.

So main problem still seems to be "kernel should not depend on
userland services during suspend", refrigerator or not.
Pavel
--
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