From: Benjamin Herrenschmidt Subject: Re: [PATCH v3 03/17] powerpc: Add PFO support to the VIO bus Date: Fri, 11 May 2012 07:58:18 +1000 Message-ID: <1336687098.3881.63.camel@pasglop> References: <1334242825.18090.4.camel@key-ThinkPad-W510> <1334243302.18090.10.camel@key-ThinkPad-W510> <1335841603.3621.8.camel@pasglop> <20120510190835.GB12304@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Kent Yoder , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linuxppc-dev@lists.ozlabs.org To: Robert Jennings Return-path: Received: from gate.crashing.org ([63.228.1.57]:36048 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761686Ab2EJV61 (ORCPT ); Thu, 10 May 2012 17:58:27 -0400 In-Reply-To: <20120510190835.GB12304@linux.vnet.ibm.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Thu, 2012-05-10 at 14:08 -0500, Robert Jennings wrote: > * Benjamin Herrenschmidt (benh@kernel.crashing.org) wrote: > > Is this meant to be called in atomic context ? If not, maybe it should > > at the very least do a cond_resched() ? > > > > Else, what about ceding the processor ? Or at the very least reducing > > the thread priority for a bit ? > > > > Shouldn't we also enforce to always have a timeout ? IE. Something like > > 30s or so if nothing specified to avoid having the kernel just hard > > lock... > > > > In general I don't like that sort of synchronous code, I'd rather return > > the busy status up the chain which gives a chance to the caller to take > > more appropriate measures depending on what it's doing, but that really > > depends what you use that synchronous call for. I suppose if it's for > > configuration type operations, it's ok... > > This function is called in atomic context, it is used by PFO-type device > drivers to perform operations with the nest accelerator unit (like > crypto acceleration). > > Having the timeout and retries in this function is the wrong thing to do. > We'll resubmit this without the loop and the caller will be responsible for > retrying the operations. > > I would rather have the caller cede the processor or alter thread > priority where appropriate than doing that in this function. I don't > think this should be done in this crypto driver. That sounds right indeed... as long as the upper crypto layer has a concept of "try again later"... if it doesn't it will result in random funny failures :-) Cheers, Ben.