Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932805Ab1D1RKk (ORCPT ); Thu, 28 Apr 2011 13:10:40 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:50240 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759646Ab1D1RKj (ORCPT ); Thu, 28 Apr 2011 13:10:39 -0400 Date: Thu, 28 Apr 2011 18:10:20 +0100 From: Russell King - ARM Linux To: Viresh Kumar Cc: vinod.koul@intel.com, dan.j.williams@intel.com, armando.visconti@st.com, linux-kernel@vger.kernel.org, shiraz.hashim@st.com, viresh.linux@gmail.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH V3 2/7] dmaengine/dw_dmac: Replace spin_lock* with irqsave variants Message-ID: <20110428171020.GB17290@n2100.arm.linux.org.uk> References: <50dc2f47f2c9f94fce78583568830a66af49307d.1303896567.git.viresh.kumar@st.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50dc2f47f2c9f94fce78583568830a66af49307d.1303896567.git.viresh.kumar@st.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1750 Lines: 46 On Wed, Apr 27, 2011 at 03:06:44PM +0530, Viresh Kumar wrote: > @@ -407,6 +410,8 @@ EXPORT_SYMBOL(dw_dma_get_dst_addr); > static void dwc_handle_cyclic(struct dw_dma *dw, struct dw_dma_chan *dwc, > u32 status_block, u32 status_err, u32 status_xfer) > { > + unsigned long flags; > + > if (status_block & dwc->mask) { > void (*callback)(void *param); > void *callback_param; > @@ -418,9 +423,9 @@ static void dwc_handle_cyclic(struct dw_dma *dw, struct dw_dma_chan *dwc, > callback = dwc->cdesc->period_callback; > callback_param = dwc->cdesc->period_callback_param; > if (callback) { > - spin_unlock(&dwc->lock); > + spin_unlock_irqrestore(&dwc->lock, flags); > callback(callback_param); > - spin_lock(&dwc->lock); > + spin_lock_irqsave(&dwc->lock, flags); I'm really not convinced that this is anywhere near correct. I'm surprised this doesn't spit out a compiler warning. spin_unlock_irqrestore() reads the flags argument and puts it into the PSR. spin_lock_irqsave() reads the PSR, puts it into the flags argument, sets the interrupt mask bit and writes back to the PSR. So, if you do: unsigned long flags; spin_unlock_irqrestore(&dwc->lock, flags); ... spin_lock_irqsave(&dwc->lock, flags); you're going to end up corrupting the PSR. In any case, releasing a spinlock temporarily within a called function is _really_ not a nice thing to do. It makes code review rather difficult as called functions become non-atomic when called within an atomic region. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/