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=-5.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 54BEFC4346E for ; Thu, 24 Sep 2020 08:45:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1BCDD21D91 for ; Thu, 24 Sep 2020 08:45:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="qRbvu818" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727274AbgIXIp5 (ORCPT ); Thu, 24 Sep 2020 04:45:57 -0400 Received: from mx2.suse.de ([195.135.220.15]:50566 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726387AbgIXIp5 (ORCPT ); Thu, 24 Sep 2020 04:45:57 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600937156; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LiDYwk9lySi3d8BWgZSBd7bGIz2hU9PObtVbPv44pU0=; b=qRbvu818hxb4yQXYEV6arBnycD4gPXoawp779lJY5QVHURh4kC+3d4wN4aM9tKR16SzLl6 npXu34KsVvaEvmIm60mGfnbYEio2ElAPs7oB5CEl23vZc32ZiGCUKbAgGIzxu4Y8ethp/X DPPYc78oNBZZwdXp91VbUq0oC7VyIl4= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 40316AD6B; Thu, 24 Sep 2020 08:46:34 +0000 (UTC) Date: Thu, 24 Sep 2020 10:45:55 +0200 From: Petr Mladek To: Sergey Senozhatsky Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH printk 3/5] printk: use buffer pool for sprint buffers Message-ID: <20200924084555.GJ6442@alley> References: <20200922153816.5883-1-john.ogness@linutronix.de> <20200922153816.5883-4-john.ogness@linutronix.de> <20200923151129.GC6442@alley> <20200924054058.GE577@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924054058.GE577@jagdpanzerIV.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2020-09-24 14:40:58, Sergey Senozhatsky wrote: > On (20/09/23 17:11), Petr Mladek wrote: > > > > AFAIK, there is one catch. We need to use va_copy() around > > the 1st call because va_format can be proceed only once. > > > > Current printk() should be good enough for reporting, say, "Kernel > stack overflow" errors. Is extra pressure that va_copy() adds something > that we need to consider? The thing is that vsprintf() traverses the arguments using va_arg(). It modifies internal values so that the next va_arg() will read the next value. If we want to call vsprintf() twice then we need to reset the internal va_list states. My understanding is that va_copy() is the only legal way when we are already nested inside va_start()/va_end(). See also the commit 5756b76e4db643d8f7 ("vsprintf: make %pV handling compatible with kasprintf()"). Best Regards, Petr