From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 08/16] dma-debug: add core checking functions Date: Sun, 11 Jan 2009 09:34:02 +0100 Message-ID: <20090111083402.GN9466@8bytes.org> References: <1231517970-20288-1-git-send-email-joerg.roedel@amd.com> <1231517970-20288-9-git-send-email-joerg.roedel@amd.com> <20090110231127.GK17917@elte.hu> <20090111075752.GI9466@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: iommu@lists.linux-foundation.org, mingo@redhat.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: Ingo Molnar Return-path: Received: from 8bytes.org ([88.198.83.132]:33477 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750836AbZAKIeF (ORCPT ); Sun, 11 Jan 2009 03:34:05 -0500 Content-Disposition: inline In-Reply-To: <20090111075752.GI9466@8bytes.org> Sender: netdev-owner@vger.kernel.org List-ID: On Sun, Jan 11, 2009 at 08:57:52AM +0100, Joerg Roedel wrote: > On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote: > > > > * Joerg Roedel wrote: > > > > > +#define err_printk(dev, format, arg...) do { \ > > > + error_count += 1; \ > > > + if (show_all_errors || show_num_errors > 0) { \ > > > + WARN(1, "%s %s: " format, \ > > > + dev_driver_string(dev), \ > > > + dev_name(dev) , ## arg); \ > > > + } \ > > > + if (!show_all_errors && show_num_errors > 0) \ > > > + show_num_errors -= 1; \ > > > > Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket > > so if two errors hit at once on two CPUs then the error tracking variables > > can be accessed at once. > > > > I'd suggest a simple global lock for this error case (taken inside the > > hash bucket lock), to be on the safe side. > > > > Also, please dont use a macro for this - printk details can be passed in > > to helper inlines/functions too. > > Yeah, this is not SMP-safe, I know. But debugfs does not support > atomic_t so I made the variables u32. But at least a race condition has > not a too bad impact. What may habben is that error_count misses a error > or the show_num_errors become negative. > But if we really want to avoid this I think its better to add atomic_t > support to debugfs. What do you think? Even a global lock will not really help here because show_num_errors and show_all_errors can be set using debugfs. Either we live with the small race (with limited impact) or I add atomic_t support to debugfs. Joerg