linux-kernel - Re: [PATCH 00/10 v2] iommu/amd: lock splitting & GFP

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Message-ID: <1521499764.3722.108.camel@redhat.com>
Date:   Mon, 19 Mar 2018 17:49:24 -0500
From:   Scott Wood <swood@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH 00/10 v2] iommu/amd: lock splitting & GFP_KERNEL
 allocation

On Mon, 2018-03-19 at 13:15 +0100, Sebastian Andrzej Siewior wrote:
> On 2018-03-17 16:43:39 [-0500], Scott Wood wrote:
> > If that's worth the lock dropping then fine (though why does only
> > one
> > of the two allocations use GFP_KERNEL?), but it doesn't need to be
> > a
> 
> That was a mistake, I planned to keep both as GFP_KERNEL.
> 
> > raw lock if the non-allocating users are separated.  Keeping them
> > separate will also preserve the WARNs if we somehow end up in an
> > atomic
> > context with no table (versus relying on atomic sleep debugging
> > that
> > may or may not be enabled), and make the code easier to understand
> > by
> > being explicit about which functions can be used from RT-atomic
> > context.
> 
> That separated part is okay. We could keep it. However, I am not sure
> if
> looking at the table irq_lookup_table[devid] without the lock is
> okay.
> The pointer is assigned without DTE entry/iommu-flush to be
> completed. 
> This does not look "okay".

Those callers are getting the devid from an irq_2_irte struct, which
was set up in irq_remapping_alloc() after get/alloc_irq_table() is
completed.

-Scott