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

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Message-Id: <E1Kuxk4-0006NT-Ie@pomaz-ex.szeredi.hu>
Date:	Wed, 29 Oct 2008 00:12:52 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	ncunningham@...a.org.au
CC:	miklos@...redi.hu, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] Freezer: Don't count threads waiting for
	frozen	filesystems.

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.

Miklos
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