From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 417ADC001DF for ; Fri, 21 Jul 2023 16:00:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229652AbjGUQAw (ORCPT ); Fri, 21 Jul 2023 12:00:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231709AbjGUQAv (ORCPT ); Fri, 21 Jul 2023 12:00:51 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5290F30DD; Fri, 21 Jul 2023 09:00:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C07C361D26; Fri, 21 Jul 2023 16:00:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2B74C433C7; Fri, 21 Jul 2023 16:00:44 +0000 (UTC) Date: Fri, 21 Jul 2023 12:00:40 -0400 From: Steven Rostedt To: Alexander Lobakin Cc: Peter Zijlstra , LKML , Ingo Molnar , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , "Benjamin Herrenschmidt" , Paul Mackerras , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , , "H. Peter Anvin" , Josh Poimboeuf , "Jiri Kosina" , Miroslav Benes , Petr Mladek , Joe Lawrence , Colin Ian King , Masami Hiramatsu , "Nicholas Piggin" , Jisheng Zhang , , , , , , =?UTF-8?B?546L6LSH?= , Guo Ren , Jakub Kicinski Subject: Re: [PATCH] tracing: Have all levels of checks prevent recursion Message-ID: <20230721120040.6ed2c02a@gandalf.local.home> In-Reply-To: <1b402c0c-1beb-d93f-ff6d-955350995ca3@intel.com> References: <20211015110035.14813389@gandalf.local.home> <20211015161702.GF174703@worktop.programming.kicks-ass.net> <20211015133504.6c0a9fcc@gandalf.local.home> <20211015135806.72d1af23@gandalf.local.home> <20211015180429.GK174703@worktop.programming.kicks-ass.net> <20211015142033.72605b47@gandalf.local.home> <20211015142541.4badd8a9@gandalf.local.home> <1b402c0c-1beb-d93f-ff6d-955350995ca3@intel.com> X-Mailer: Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Fri, 21 Jul 2023 17:34:41 +0200 Alexander Lobakin wrote: > From: Steven Rostedt > Date: Fri, 15 Oct 2021 14:25:41 -0400 > > Sorry for such a necroposting :z > Just wanted to know if this is a bug, so that I could send a fix, or > intended behaviour. > > > On Fri, 15 Oct 2021 14:20:33 -0400 > > Steven Rostedt wrote: > > > >>> I think having one copy of that in a header is better than having 3 > >>> copies. But yes, something along them lines. > >> > >> I was just about to ask you about this patch ;-) > > > > Except it doesn't build :-p (need to move the inlined function down a bit) > > > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > > index 4d244e295e85..b32e3dabe28b 100644 > > --- a/include/linux/preempt.h > > +++ b/include/linux/preempt.h > > @@ -77,6 +77,27 @@ > > /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */ > > #include > > > > +/** > > + * interrupt_context_level - return interrupt context level > > + * > > + * Returns the current interrupt context level. > > + * 0 - normal context > > + * 1 - softirq context > > + * 2 - hardirq context > > + * 3 - NMI context > > + */ > > +static __always_inline unsigned char interrupt_context_level(void) > > +{ > > + unsigned long pc = preempt_count(); > > + unsigned char level = 0; > > + > > + level += !!(pc & (NMI_MASK)); > > + level += !!(pc & (NMI_MASK | HARDIRQ_MASK)); > > + level += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)); > > This doesn't take into account that we can switch the context manually > via local_bh_disable() / local_irq_save() etc. During the testing of the You cannot manually switch interrupt context. > separate issue[0], I've found that the function returns 1 in both just > softirq and softirq under local_irq_save(). > Is this intended? Shouldn't that be That is intended behavior. local_bh_disable() and local_irq_save() is not a context switch. It is just preventing that context from happening. The interrupt_context_level() is to tell us what context we are running in, not what context is disabled. > > level += !!(pc & (NMI_MASK)); > level += !!(pc * (NMI_MASK | HARDIRQ_MASK)) || irqs_disabled(); > level += !!(pc * (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)) || > in_atomic(); > > ? > Otherwise, the result it returns is not really "context level". local_bh_disable() use to (and perhaps still does in some configurations) confuse things. But read the comment in kernel/softirq.c /* * SOFTIRQ_OFFSET usage: * * On !RT kernels 'count' is the preempt counter, on RT kernels this applies * to a per CPU counter and to task::softirqs_disabled_cnt. * * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq * processing. * * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET) * on local_bh_disable or local_bh_enable. * * This lets us distinguish between whether we are currently processing * softirq and whether we just have bh disabled. */ Just because you disable interrupts does not mean you are in interrupt context. -- Steve > > > + > > + return level; > > +} > > + > [0] > https://lore.kernel.org/netdev/b3884ff9-d903-948d-797a-1830a39b1e71@intel.com > > Thanks, > Olek