linux-kernel - Re: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems.

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Message-Id: <1225229399.9661.13.camel@nigel-laptop>
Date:	Wed, 29 Oct 2008 08:29:59 +1100
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	rjw@...k.pl, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] Freezer: Don't count threads waiting for frozen
	filesystems.

Hi.

On Tue, 2008-10-28 at 21:25 +0100, Miklos Szeredi wrote:
> > To deal with requests that are already in progress, I'd suggest three
> > possibilities, in the order I think they should be preferred.
> > 
> > 1) Use wait_event_freezeable[_timeout] in fuse code. Probably preferable
> > to #2, but I thought of it later :)
> > 
> > 2) Use freezer_do_not_count as part of FUSE_MIGHT_FREEZE (resetting
> > before exiting the callers, of course). If the request doesn't complete
> > during the freezing period, it must be because the userspace thread was
> > already frozen. If the request does complete, we're counted again during
> > the normal freezing of userspace that follows the freezing of
> > filesystems.
> > 
> > 3) Adding a means to check whether processes being frozen are fuse
> > requests. The code could then wait for fc->num_waiting - (say)
> > fc->num_frozen == 0.
> 
> Yup, these fix the freezing of tasks which have outstanding fuse
> requests.
> 
> However it does not fix the freezing of tasks which are waiting for
> VFS locks (i.e. inode->i_mutex) held by the outstanding fuse requests.
> This is the tricky part...

Convert them all to wait_event_freezeable. If you know the locks they're
waiting on definitely aren't going to be free until post-resume and
we're going to be trying to freeze them while they're waiting, that
would be the right behaviour.

Regards,

Nigel

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