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

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Message-Id: <1225235860.9661.42.camel@nigel-laptop>
Date:	Wed, 29 Oct 2008 10:17:40 +1100
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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 Wed, 2008-10-29 at 00:12 +0100, Miklos Szeredi wrote:
> On Wed, 29 Oct 2008, Nigel Cunningham wrote:
> > > 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...
> > 
> > Okay. Looking back on our conversation brought me back to this message,
> > which I think needs another reply.
> > 
> > If we take the strategy of holding new requests and allowing existing
> > ones to complete, then am I right in thinking that we only need to worry
> > about where inode->i_mutex is taken in fs/fuse/file.c (I don't see it
> > taken in other fs/fuse/*.c files).
> 
> Nope, i_mutex is usually taken by the VFS not the filesystem.  That
> means that the filesystem is called with the mutex already held.  Try
> "grep i_mutex fs/*.c".  There's also sb->s_vfs_rename_mutex, for all
> the gory details see Documentation/filesystems/Locking.
> 
> So it's not just having to fix fuse, it's having to "fix" the VFS as
> well.

Remember, though, that we're only freezing fuse at the moment, and
strictly one filesystem at a time. We can thus happily wait for the
i_mutex taken by some other process to be released.

Regards,

Nigel

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