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 X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E39FC4707A for ; Fri, 21 May 2021 19:45:33 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C6CFA613D9 for ; Fri, 21 May 2021 19:45:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C6CFA613D9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=rNY96uqvSal+95QCCCBhEPR9gWxlf5msT+MTw/kXUGQ=; b=XXOVDmWAq0jVvHwWJi5Jj2lzNr nGdrh8Lta5qbYsaUI2Ve+kqocWgtOjrokc8F1jzZINRMixqs9jiGW8Qr4/YKA0lerw1iPuJoQInyl XTivygfp7bzflo1WGhhtA3ZAYgLmcuyTCptZ9mSrdpNyzgMLNiG06tgIiyGlTjozkxHGtXnCOEdxS mpWYVEmyS8jRYnzt6+Nf+37gJcutrBxAgBUoj+RQN1eF+pBtKb2lMQeCBRYvdGz8emX/T7ElcWVXi IaJbfAF3YvwvaPPwp+Bieieuq5M2740fAtHsa6Ja+7Z+K/891OiPnbdOeNhj5asEsgVWsyhmNzojl zYIGrjNw==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lkB3k-000ure-Dm; Fri, 21 May 2021 19:43:49 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lkB22-000uG6-8T for linux-arm-kernel@desiato.infradead.org; Fri, 21 May 2021 19:42:02 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description; bh=sVvcxbQSfAemZf/h/BWHu58ipxMHsNFFKvAp7FMao3I=; b=ODMVckacOBkNCieOOuaL5mgige QMow4F/7d2zEBbLmwjPDBGyP3oqcqOWomTQR7UaxOdtT6vq+/KendEt2NZ+EzzOyiXfMyDxCDNOGc TM8Jz+VU2Nm2u1q0jZczfFv5q6zKvyHZlGTrMF4olcmYVMVD8X1CpsFOL4s3UBxT+BOJplL+tp8hB HjDlRiSmEFXOQAaxnFu9K09JlNN2E/rjUmMlvq9c5YegLd7v3yWfT62bDQquCE6GCbiFij93ITRIJ 3ilD2Q8W5uLis5NlZI7kptF+J7XpbJfynAMFu94kvQlcjZBiWlNsYfzyC1t7QU9OVnkuugtplfYx8 1jNMGkog==; Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lkB1z-00HO2r-GC for linux-arm-kernel@lists.infradead.org; Fri, 21 May 2021 19:42:00 +0000 Received: from [192.168.254.32] (unknown [47.187.214.213]) by linux.microsoft.com (Postfix) with ESMTPSA id 81D2120B7188; Fri, 21 May 2021 12:41:57 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 81D2120B7188 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1621626118; bh=sVvcxbQSfAemZf/h/BWHu58ipxMHsNFFKvAp7FMao3I=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=NI/hYFDEvvsCn23V5INEa9b8dTn2BppIDjflkBxVCslto7/I7DbLEs2m9XN5og4yC oHP5is8Jke0hB6M2MISMT2cjSTuef18UEjo+FwH+/YQU1DLlSOTA032lcn4cZ4uoBC FBpmEg7f1Xy2eFtvPKyJiYl6l5sDLEOC0CYv3TPg= Subject: Re: [RFC PATCH v4 1/2] arm64: Introduce stack trace reliability checks in the unwinder To: Josh Poimboeuf Cc: Mark Brown , mark.rutland@arm.com, ardb@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210516040018.128105-1-madvenka@linux.microsoft.com> <20210516040018.128105-2-madvenka@linux.microsoft.com> <20210521161117.GB5825@sirena.org.uk> <20210521174242.GD5825@sirena.org.uk> <26c33633-029e-6374-16e6-e9418099da95@linux.microsoft.com> <20210521175318.GF5825@sirena.org.uk> <20210521184817.envdg232b2aeyprt@treble> <74d12457-7590-bca2-d1ce-5ff82d7ab0d8@linux.microsoft.com> <20210521191140.4aezpvm2kruztufi@treble> <20210521191608.f24sldzhpg3hyq32@treble> From: "Madhavan T. Venkataraman" Message-ID: Date: Fri, 21 May 2021 14:41:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210521191608.f24sldzhpg3hyq32@treble> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210521_124159_618094_0E93A4FC X-CRM114-Status: GOOD ( 20.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 5/21/21 2:16 PM, Josh Poimboeuf wrote: > On Fri, May 21, 2021 at 02:11:45PM -0500, Josh Poimboeuf wrote: >> On Fri, May 21, 2021 at 01:59:16PM -0500, Madhavan T. Venkataraman wrote: >>> >>> >>> On 5/21/21 1:48 PM, Josh Poimboeuf wrote: >>>> On Fri, May 21, 2021 at 06:53:18PM +0100, Mark Brown wrote: >>>>> On Fri, May 21, 2021 at 12:47:13PM -0500, Madhavan T. Venkataraman wrote: >>>>>> On 5/21/21 12:42 PM, Mark Brown wrote: >>>>> >>>>>>> Like I say we may come up with some use for the flag in error cases in >>>>>>> future so I'm not opposed to keeping the accounting there. >>>>> >>>>>> So, should I leave it the way it is now? Or should I not set reliable = false >>>>>> for errors? Which one do you prefer? >>>>> >>>>>> Josh, >>>>> >>>>>> Are you OK with not flagging reliable = false for errors in unwind_frame()? >>>>> >>>>> I think it's fine to leave it as it is. >>>> >>>> Either way works for me, but if you remove those 'reliable = false' >>>> statements for stack corruption then, IIRC, the caller would still have >>>> some confusion between the end of stack error (-ENOENT) and the other >>>> errors (-EINVAL). >>>> >>> >>> I will leave it the way it is. That is, I will do reliable = false on errors >>> like you suggested. >>> >>>> So the caller would have to know that -ENOENT really means success. >>>> Which, to me, seems kind of flaky. >>>> >>> >>> Actually, that is why -ENOENT was introduced - to indicate successful >>> stack trace termination. A return value of 0 is for continuing with >>> the stack trace. A non-zero value is for terminating the stack trace. >>> >>> So, either we return a positive value (say 1) to indicate successful >>> termination. Or, we return -ENOENT to say no more stack frames left. >>> I guess -ENOENT was chosen. >> >> I see. So it's a tri-state return value, and frame->reliable is >> intended to be a private interface not checked by the callers. > > Or is frame->reliable supposed to be checked after all? Looking at the > code again, I'm not sure. > > Either way it would be good to document the interface more clearly in a > comment above the function. > So, arch_stack_walk_reliable() would do this: start_backtrace(frame); while (...) { if (!frame->reliable) return error; consume_entry(...); ret = unwind_frame(...); if (ret) break; } if (ret == -ENOENT) return success; return error; Something like that. I will add a comment about all of this in the unwinder. Thanks! Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel