linux-kernel - Re: Broken pci_block_user_cfg

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Message-ID: <4E5BDEAB.5000405@siemens.com>
Date:	Mon, 29 Aug 2011 20:47:07 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Brian King <brking@...ibm.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	"Hans J. Koch" <hjk@...sjkoch.de>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: Broken pci_block_user_cfg_access interface

On 2011-08-29 17:42, Jan Kiszka wrote:
> I still don't get what prevents converting ipr to allow plain mutex
> synchronization. My vision is:
>  - push reset-on-error of ipr into workqueue (or threaded IRQ?)

I'm starting to like your proposal: I had a look at ipr, but it turned
out to be anything but trivial to convert that driver. It runs its
complete state machine under spin_lock_irq, and the functions calling
pci_block/unblock_user_cfg_access are deep inside this thing. I have no
hardware to test whatever change, and I feel a bit uncomfortable asking
Brian to redesign his driver that massively.

So back to your idea: I would generalize pci_block_user_cfg_access to
pci_block_cfg_access. It should fail when some other site already holds
the access lock, but it should remain non-blocking - for the sake of ipr.

We should still provide generic pci-2.3 IRQ masking services, but that
could be done in a second step. I could have a look at this.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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