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

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Date:	Tue, 8 Aug 2006 16:02:31 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Paolo Giarrusso <blaisorblade@...oo.it>
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

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.

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

> 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.

				Jeff
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