linux-kernel - Re: [PATCH] iommu/amd: fix accounting of device

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Message-ID: <20141112140247.GU10744@8bytes.org>
Date:	Wed, 12 Nov 2014 15:02:47 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Oded Gabbay <oded.gabbay@....com>
Cc:	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: fix accounting of device_state

On Mon, Nov 10, 2014 at 12:21:39PM +0200, Oded Gabbay wrote:
> This patch fixes a bug in the accounting of the device_state.
> In the current code, the device_state was put (decremented) too many times,
> which sometimes lead to the driver getting stuck permanently in
> put_device_state_wait(). That happen because the device_state->count would go
> below zero, which is never supposed to happen.
> 
> The root cause is that the device_state was decremented in put_pasid_state()
> and put_pasid_state_wait() but also in all the functions that call those
> functions. Therefore, the device_state was decremented twice in each of these
> code paths.
> 
> The fix is to decouple the device_state accounting from the pasid_state
> accounting - remove the call to put_device_state() from the
> put_pasid_state() and the put_pasid_state_wait())

Right, there was a double drop of the reference to device state. An
alternative would have been to remove the put_device_state call at the
end of the amd_iommu_unbind_pasid() function. But this patch works as
well and is slightly better, so: Applied, thanks.


	Joerg

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