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 6188FC4332F for ; Wed, 23 Feb 2022 07:50:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238802AbiBWHuZ (ORCPT ); Wed, 23 Feb 2022 02:50:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234276AbiBWHuY (ORCPT ); Wed, 23 Feb 2022 02:50:24 -0500 Received: from mail-pj1-x1034.google.com (mail-pj1-x1034.google.com [IPv6:2607:f8b0:4864:20::1034]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C6A86D1B9 for ; Tue, 22 Feb 2022 23:49:58 -0800 (PST) Received: by mail-pj1-x1034.google.com with SMTP id j10-20020a17090a94ca00b001bc2a9596f6so1940111pjw.5 for ; Tue, 22 Feb 2022 23:49:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:user-agent:in-reply-to:references :message-id:mime-version:content-transfer-encoding; bh=E627RUNZI8BVu7aKzkB9EQU+HaYuIF8E1n5hAwi8GVI=; b=UhqSJ2zS5M8ZUtUHuH6t9qQu4lgWEU8YXCYrKcOaIeEMUDWkreFKvOOHIZu+3397hg RmMYQiZubfgjjm14Zk6D4fhr5sUY0f+1bdT2v7QCDpLQwZlGx7eTXJRc3FLW/l9lLA4a 60opWRg2r3Y+fSFqq31WqhOUpbpJH+jbO3C1s= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:user-agent:in-reply-to :references:message-id:mime-version:content-transfer-encoding; bh=E627RUNZI8BVu7aKzkB9EQU+HaYuIF8E1n5hAwi8GVI=; b=zE7brgI/+dYjR0O/0GWvbAQVseAkZzed0C2WML0bD7Wb3LuZY6/UOsHFb3q3DeFyId rWkmsvOfjyERrWuHWAsHU4Ch3g22PiiqQpGYVY1rjwW/MmzjQyKy5npJfvnaYm3k2ZNL F2WeLvttk7zi12jxTyXmpxRBnlbnn0Q+sGD2lab5h+CoXWcvqbj52nypKzM+Bnhk1nLY MZB8gPIQ7sVf8xX47WuXDpf2GmUQ8BhXijby9cSbNN53H4MQLDdsVlo4Nlj5G0X/NyDk zdSJwDS963bhmB6nu99sbtX6T5MoZYPfFlGqxOZEpj/Dmjd31yTM1/1UPMmwtbIJ2L9V pfpA== X-Gm-Message-State: AOAM533lvkjT3sDTfsAqCRtZp8ySxZ7vZCtAZJzv+30UXKKWzmpIuvIu MYZwKh5N1RCUx5QxLJ+WAZNang== X-Google-Smtp-Source: ABdhPJzZcoICgoXFEPRWRrS1CdNR8/GchBf+zvOrVpytglbEK2XtyhsZd1JBznLxucmnfNejVvFwFw== X-Received: by 2002:a17:90b:197:b0:1bc:5037:7c52 with SMTP id t23-20020a17090b019700b001bc50377c52mr7964776pjs.174.1645602597667; Tue, 22 Feb 2022 23:49:57 -0800 (PST) Received: from [127.0.0.1] (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id e10sm5221699pgw.16.2022.02.22.23.49.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Feb 2022 23:49:57 -0800 (PST) Date: Tue, 22 Feb 2022 23:49:54 -0800 From: Kees Cook To: Jann Horn , Anton Vorontsov , Colin Cross , Tony Luck , Ard Biesheuvel CC: Sebastian Andrzej Siewior , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v2=5D_pstore=3A_Don=27t_use_sem?= =?US-ASCII?Q?aphores_in_always-atomic-context_code?= User-Agent: K-9 Mail for Android In-Reply-To: <20220218181950.1438236-1-jannh@google.com> References: <20220218181950.1438236-1-jannh@google.com> Message-ID: <8D85619E-99BD-4DB5-BDDB-A205B057C910@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On February 18, 2022 10:19:50 AM PST, Jann Horn wrote= : >pstore_dump() is *always* invoked in atomic context (nowadays in an RCU >read-side critical section, before that under a spinlock)=2E >It doesn't make sense to try to use semaphores here=2E Ah, very nice=2E Thanks for the analysis! >[=2E=2E=2E] >-static bool pstore_cannot_wait(enum kmsg_dump_reason reason) >+bool pstore_cannot_block_path(enum kmsg_dump_reason reason) Why the rename, extern, and EXPORT? This appears to still only have the sa= me single caller? > [=2E=2E=2E] >- pr_err("dump skipped in %s path: may corrupt error record\n", >- in_nmi() ? "NMI" : why); >- return; >- } >- if (down_interruptible(&psinfo->buf_lock)) { >- pr_err("could not grab semaphore?!\n"); >+ if (pstore_cannot_block_path(reason)) { >+ if (!spin_trylock_irqsave(&psinfo->buf_lock, flags)) { >+ pr_err("dump skipped in %s path because of concurrent dump\n" >+ , in_nmi() ? "NMI" : why); The pr_err had the comma following the format string moved, and the note a= bout corruption removed=2E Is that no longer accurate? Otherwise looks good; thank you! --=20 Kees Cook