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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 E93F4C43144 for ; Thu, 28 Jun 2018 02:55:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9F942257C5 for ; Thu, 28 Jun 2018 02:55:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="PpOMGRp6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F942257C5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932761AbeF1CzX (ORCPT ); Wed, 27 Jun 2018 22:55:23 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:32957 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932322AbeF1CzR (ORCPT ); Wed, 27 Jun 2018 22:55:17 -0400 Received: by mail-pg0-f66.google.com with SMTP id e11-v6so1794969pgq.0; Wed, 27 Jun 2018 19:55:17 -0700 (PDT) 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:user-agent; bh=skCbf+DfXdqw9S/HcSge1QOD7NgcjCH4BdVpJ466xIM=; b=PpOMGRp6cgf4gCXTZf/k4N+j1RFB/Hu4wXskTxKuyn5oVl5/nRllrlqw8+dq9t6eKA rPwRZ+u/lkUKA63bAPXi1u0s+uAxNoFnq5gH4WFYsy89Ko4q6+sZlY3bcqLxG1xHRjrM 7MtX22YNTT04pXiH2SrLFU/MNnDa/jBhJEaTS3k0OwU1OjX54QUbW59MfRhu/OSnff4e 1btH+cn8RYVzfbTWnK2xLQ+1CsFTiJPrk1ZgbbupZMMzUINQFib8t8P1B2cn2YRXwm+B Qo5DfTnK+GPI3va+ENPg3AtxR8gM5C0wbGVZi4ZLQ9AP3BEOGNCTFPjTjPNL/rFJUT4R pOQA== 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:user-agent; bh=skCbf+DfXdqw9S/HcSge1QOD7NgcjCH4BdVpJ466xIM=; b=Yk1avL05FaKseRty6KtQkyivznKcv2mLlcE6gzOLrWTNftutF+tqESCJLsOh/njC1A +FrPSe6nkb1Vnb7w3isjNQ7aMlSkBZe866euuHL1JWPFBx6wYeqct53l4vGVNfXDrZUP aR1xPo4uTJJDWMhDNV7Ti3iVzVE+FXLqPAeAZ9yoAA9myQrQZWbYSxyTesyvID0oOg8j +exLOIN8yooESAFiuwATSNg0UzemhQMZr87u8BeHdDHff0Pgz5Cw47IXqGHMOeAGdkw6 T18dJ0sIa1+hrrlP7oPGtwLlPcyMFEBhM1WUfEeTtWwuhJUFe54xmugQryWSypk1J9FQ dT2w== X-Gm-Message-State: APt69E3gaePv4coKenwJoCD3ETi6ZnSc7FM2wFUapzGss5c0qgiGfCNI aELq5tk+OMqKI0mzslD+oVhGcDP/ X-Google-Smtp-Source: AAOMgpdYUZU5QBlOunr1DIlC8iTsB86aZiGlxOyQVNCapTipn15vscP87sAsBdEtRR60OrIxSN7Brg== X-Received: by 2002:a63:4386:: with SMTP id q128-v6mr1096162pga.353.1530154517074; Wed, 27 Jun 2018 19:55:17 -0700 (PDT) Received: from localhost ([110.70.27.221]) by smtp.gmail.com with ESMTPSA id u1-v6sm7820302pfn.59.2018.06.27.19.55.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 27 Jun 2018 19:55:15 -0700 (PDT) Date: Thu, 28 Jun 2018 11:55:12 +0900 From: Sergey Senozhatsky To: Linus Torvalds , One Thousand Gnomes , Steven Rostedt Cc: Sergey Senozhatsky , Petr Mladek , Greg Kroah-Hartman , Jiri Slaby , Peter Zijlstra , Andrew Morton , Dmitry Vyukov , Linux Kernel Mailing List , linux-serial , SergeySenozhatsky Subject: Re: [RFC][PATCH 0/6] Use printk_safe context for TTY and UART port locks Message-ID: <20180628025512.GF481@jagdpanzerIV> References: <20180615093919.559-1-sergey.senozhatsky@gmail.com> <20180618143818.50b2f2f9@alans-desktop> <20180619005308.GA405@jagdpanzerIV> <20180619083021.4avsgvcqjrpkat6s@pathway.suse.cz> <20180620025050.GE650@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (06/20/18 12:38), Linus Torvalds wrote: > On Wed, Jun 20, 2018 at 11:50 AM Sergey Senozhatsky > wrote: > > > > It's not UART on its own that immediately calls into printk(), that would > > be trivial to fix, it's all those subsystems that serial console driver > > can call into. > > We already have the whole PRINTK_SAFE_CONTEXT_MASK model that only > adds it to a secondary buffer if you get recursion. Why isn't that > triggering? That's the whole point of it. Linus, Alan, Steven, are you on board with the patch set? What shall I do to improve it? PRINTK_SAFE_CONTEXT_MASK is what we answer nowadays when someone says "printk causes deadlocks". We really can't remove all printk-s that can cause uart->...->printk->uart recursion, and the only other option is to use spin_trylock on uart_port->lock in every driver and discard con->write() if we see that we have re-entered uart. I'd rather use per-CPU printk_safe buffer in this case. -ss