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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5290AC4361B for ; Wed, 9 Dec 2020 10:46:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13A8D23B6C for ; Wed, 9 Dec 2020 10:46:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730204AbgLIKq6 (ORCPT ); Wed, 9 Dec 2020 05:46:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58562 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728277AbgLIKq5 (ORCPT ); Wed, 9 Dec 2020 05:46:57 -0500 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC3F5C0613CF for ; Wed, 9 Dec 2020 02:46:17 -0800 (PST) Received: by mail-pf1-x443.google.com with SMTP id q22so745583pfk.12 for ; Wed, 09 Dec 2020 02:46:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=13Rn7jh3b3TjSNdG/NRwwmrqyqpxZcBccJA2fkW9O6Q=; b=JMKpByMlVjcEJj9bv08rD0dOIJ/kIYPvIrrdUzhle4cH0cx6SU2BNTJ1LoH+2CeXwQ M+TDc3W+rAovxErKzyMcPUI8RcoyqPR/5KXdvrEe7L2d69j+5E9Ccrqra6/f8SA8lpfV SBAB6r5j56Voq52JfrI+5G/BAhd7jkqXPhLzKtHmB4KIf5g8/l6otdBx0sPnpgrQFv6L DHjFCpgTMTHbtbxzM8Cp+bfec8n9PTw8zO9fnYvZhSXQ+2pvow3i1gKHWYW46UcqZk9r /3flwNk+xboF8niYe21SpQxTU+f2vV6QJkPRwy3Agrd8dfISpPo1ZYASb1fOlfB2/iNs LGRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=13Rn7jh3b3TjSNdG/NRwwmrqyqpxZcBccJA2fkW9O6Q=; b=JX1wTY9ZBeRpN0uMyDwKm007PIT+xBKhw3ARlzR9hCbb6kWV266pDNZOWpYpqjeelP zEeIPLfX4KGdK7dobzfRQujCPjLohyXMgS34dkCmsQwDvhIbA3dCtw6UIe5gzCV5w1zh sYdTqvYuc1i1m6dZ9huKhvc6UCVzf8ZLNeCPs79MmdDmHNpvMGAaiS2qZIbCq46KebJc ebHXIwCgQZqa/lxZIk1Zm7yhD2lToRmsW8V34V2dYJIKL7jTJK73mOseLeSj/fvx+Z49 ukBYD12Tj9p7y9s6cirSGg2mCbrKlJkBR9u344+mpWfF/8zIuUN5h/PejxLSa/S66u0Z c+9A== X-Gm-Message-State: AOAM531bhBI5tuKnJHxnqYYIty1K/cIXuOaXAbhSHL5kjdB4EpMyLHlX 76wNMesqk1eQuMMuRr6msI5SuGz8uHx6rQ== X-Google-Smtp-Source: ABdhPJz0Nuw0n2FzUX5G5rCbfjmHOibelJ45uwdQ/mRHGbVhGPxtL7nfz0Lzbkw5S3cHdNQ1LbO+dQ== X-Received: by 2002:a63:ed0b:: with SMTP id d11mr1395763pgi.261.1607510777231; Wed, 09 Dec 2020 02:46:17 -0800 (PST) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id o62sm1847186pjo.17.2020.12.09.02.46.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Dec 2020 02:46:16 -0800 (PST) Date: Wed, 9 Dec 2020 19:46:13 +0900 From: Sergey Senozhatsky To: Sergey Senozhatsky Cc: Peter Zijlstra , John Ogness , Sergey Senozhatsky , Petr Mladek , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t Message-ID: References: <20201201205341.3871-1-john.ogness@linutronix.de> <20201201205341.3871-3-john.ogness@linutronix.de> <875z5c9bhn.fsf@jogness.linutronix.de> <20201209081623.GI2414@hirez.programming.kicks-ass.net> <20201209092204.GD1667627@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201209092204.GD1667627@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/12/09 18:22), Sergey Senozhatsky wrote: > > > > Please put on your eye cancer gear and inspect the atomic implementation > > of PA-RISC, Sparc32, feh, I forgot who else. > > > > Those SMP capable architectures are gifted with just one XCHG like > > atomic instruction :/ Anyway, as said in the other email, they also > > don't have NMIs so it mostly works. PeterZ, thanks for the pointers! > Hmm, wow. OK, I definitely want to look further. > > When some CONFIG_DEBUG_FOO_BAR code wants to pr_err from prb->atomic_op > on those archs then we deadlock in printk once again? E.g. arch/sparc/lib/atomic32.c spinlock_t __atomic_hash[ATOMIC_HASH_SIZE]; atomic_foo() { spin_lock_irqsave(ATOMIC_HASH(v), flags) ... spin_unlock_irqrestore(ATOMIC_HASH(v), flags); } So another potential re-entry path is atomic_foo() spin_lock_irqsave(ATOMIC_HASH(v), flags) printk() prb() atomic_foo() spin_lock_irqsave(ATOMIC_HASH(v), flags) which can deadlock, in theory, if both atomics HASH to the same key (same spin_lock). I wonder what else am I missing. -ss