linux-kernel - Re: [PATCH 2/3] uml: fix proc-vs-interrupt context spinlock deadlock

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Message-ID: <20060809144459.58896.qmail@web25222.mail.ukl.yahoo.com>
Date:	Wed, 9 Aug 2006 16:44:59 +0200 (CEST)
From:	Paolo Giarrusso <blaisorblade@...oo.it>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Andrew Morton <akpm@...l.org>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] uml: fix proc-vs-interrupt context spinlock deadlock

Jeff Dike <jdike@...toit.com> ha scritto: 

> On Tue, Aug 08, 2006 at 12:59:05PM +0200, Paolo Giarrusso wrote:
> > I could be wrong, but I trust that thanks to deep and good work
> by
> > who designed locking in the network layer, this patch is correct.
> And
> > indeed I addressed your issues below.
> 
> OK, but there will need to be comments explaining why it is OK that
> this data only looks half-locked.

Guess I'll put it in Documentation and reference it.

> The locking, as it stands, looks consistent and conservative.
Yes, it is.
> However, there are some places where critical sections are too big
> and
> the locking should be narrowed.

Yes, in particular we cannot hold a spinlock for the whole _open
since it must call sleeping functions. 

> > This is also true of char/block devices (you don't need to lock
> > against write/read in open/close; UBD doesn't know that but I
> have
> > unfinished patches for it), but there it's simpler: if userspace
> you
> > call close while a read is executing, thanks to refcounting
> (sys_read
> > does fget) the ->close (or ->release) is only called after the
> end of
> > ->read.
> 
> In my current patchset, there is a per-queue lock which is mostly
> managed by the block layer.

I'll try then to finish the patches soon and merge them; the main
problem is splitting (including the use of different locks) normal
locking from our peculiar locking of _open/_close against mconsole
changes.

Chiacchiera con i tuoi amici in tempo reale! 
 http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com 
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