Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933080AbZFOSTs (ORCPT ); Mon, 15 Jun 2009 14:19:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932565AbZFOSTj (ORCPT ); Mon, 15 Jun 2009 14:19:39 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:46649 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757738AbZFOSTi (ORCPT ); Mon, 15 Jun 2009 14:19:38 -0400 Subject: Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic From: Peter Zijlstra To: Ingo Molnar Cc: Hugh Dickins , linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, paulus@samba.org, acme@redhat.com, efault@gmx.de, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, Linus Torvalds , Andrew Morton In-Reply-To: <20090615181555.GA11248@elte.hu> References: <1245077165.6800.497.camel@laptop> <1245080486.6800.561.camel@laptop> <1245089065.13761.19316.camel@twins> <20090615181555.GA11248@elte.hu> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Mon, 15 Jun 2009 20:19:03 +0200 Message-Id: <1245089943.13761.19334.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2336 Lines: 83 On Mon, 2009-06-15 at 20:15 +0200, Ingo Molnar wrote: > * Peter Zijlstra wrote: > > > +static int kmap_type_to_context(enum km_type type) > > +{ > > + switch (type) { > > + case KM_BOUNCE_READ: > > + return KM_CTX_USER; > > + case KM_SKB_SUNRPC_DATA: > > + return KM_CTX_USER; > > + case KM_SKB_DATA_SOFTIRQ: > > + return KM_CTX_SOFTIRQ; > > + case KM_USER0: > > + return KM_CTX_USER; > > + case KM_USER1: > > + return KM_CTX_USER; > > + case KM_BIO_SRC_IRQ: > > + return KM_CTX_IRQ; > > + case KM_BIO_DST_IRQ: > > + return KM_CTX_IRQ; > > + case KM_PTE0: > > + return KM_CTX_USER; > > + case KM_PTE1: > > + return KM_CTX_USER; > > + case KM_IRQ0: > > + return KM_CTX_IRQ; > > + case KM_IRQ1: > > + return KM_CTX_IRQ; > > + case KM_SOFTIRQ0: > > + return KM_CTX_SOFTIRQ; > > + case KM_SOFTIRQ1: > > + return KM_CTX_SOFTIRQ; > > + case KM_NMI: > > + return KM_CTX_NMI; > > + case KM_NMI_PTE: > > + return KM_CTX_NMI; > > + } > > + > > + return KM_CTX_MAX; > > why not do a very simple stack of atomic kmaps, like Hugh suggested? > > That would mean a much simpler interface: > > kaddr = kmap_atomic(page); > > no index needed. The kunmap pops the entry off the stack: > > kunmap_atomic(kaddr); > > This becomes simpler too. > > Now, a stack can be overflown by imbalance - but that's easy to > detect and existing entries are easily printed and thus the source > of the leak is easily identified. > > In my book this design beats the current enumeration of kmap types > indices hands down ... It would likely be much more robust as well, > and much more easy to extend. > > Am i missing any subtlety? The above is mostly debug code used to validate the kmap_atomic conditions. KM_CTX_NMI nests in KM_CTX_IRQ nests in KM_CTX_SOFTIRQ nests in KM_CTX_USER. And validate that we indeed are in the context specified by the type. That is, it will warn if we use KM_IRQ1 with KM_CTX_IRQ from user context. Some of this was already captured in the old kmap debug code which I removed. But yes, I should write that nicer.. /me goes clean up -- 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/