[{"id":1610080,"web_url":"http://patchwork.ozlabs.org/comment/1610080/","msgid":"<20170317050930.GB28075@kroah.com>","date":"2017-03-17T05:09:30","subject":"Re: [PATCH] tty: hvc: don't allocate a buffer for console print on\n\tstack","submitter":{"id":11800,"url":"http://patchwork.ozlabs.org/api/people/11800/","name":"Greg Kroah-Hartman","email":"gregkh@linuxfoundation.org"},"content":"On Fri, Feb 17, 2017 at 11:42:45PM +0300, Jan Dakinevich wrote:\n> The buffer is used by virtio console driver as DMA buffer. Since v4.9\n> (if VMAP_STACK is enabled) we shouldn't use the stack for DMA.\n\nYou shouldn't use 'static' data either, that's not always guaranteed to\nbe DMA-able, right?\n\n> \n> Signed-off-by: Jan Dakinevich \n> ---\n> drivers/tty/hvc/hvc_console.c | 7 ++++++-\n> 1 file changed, 6 insertions(+), 1 deletion(-)\n> \n> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c\n> index 9b5c0fb..1ce6aaf 100644\n> --- a/drivers/tty/hvc/hvc_console.c\n> +++ b/drivers/tty/hvc/hvc_console.c\n> @@ -143,10 +143,15 @@ static struct hvc_struct *hvc_get_by_index(int index)\n> static void hvc_console_print(struct console *co, const char *b,\n> \t\t\t unsigned count)\n> {\n> -\tchar c[N_OUTBUF] __ALIGNED__;\n> \tunsigned i = 0, n = 0;\n> \tint r, donecr = 0, index = co->index;\n> \n> +\t/*\n> +\t * Access to the buffer is serialized by console_sem in caller code from\n> +\t * kernel/printk/printk.c\n> +\t */\n> +\tstatic char c[N_OUTBUF] __ALIGNED__;\n\nWhat about allocating it dynamically? That's the correct thing to do.\n\nthanks,\n\ngreg k-h","headers":{"Return-Path":"","X-Original-To":["patchwork-incoming@ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":["patchwork-incoming@ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Received":["from lists.ozlabs.org (lists.ozlabs.org [103.22.144.68])\n\t(using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3vktjM2NqGz9s0Z\n\tfor ;\n\tFri, 17 Mar 2017 16:11:19 +1100 (AEDT)","from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3])\n\tby lists.ozlabs.org (Postfix) with ESMTP id 3vktjM1K1CzDqf2\n\tfor ;\n\tFri, 17 Mar 2017 16:11:19 +1100 (AEDT)","from mail.linuxfoundation.org (mail.linuxfoundation.org\n\t[140.211.169.12])\n\t(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256\n\tbits)) (No client certificate requested)\n\tby lists.ozlabs.org (Postfix) with ESMTPS id 3vktgb0yRHzDqc4\n\tfor ;\n\tFri, 17 Mar 2017 16:09:46 +1100 (AEDT)","from localhost (unknown [166.170.37.132])\n\tby mail.linuxfoundation.org (Postfix) with ESMTPSA id F26025AA;\n\tFri, 17 Mar 2017 05:09:43 +0000 (UTC)"],"Date":"Fri, 17 Mar 2017 14:09:30 +0900","From":"Greg Kroah-Hartman ","To":"Jan Dakinevich ","Subject":"Re: [PATCH] tty: hvc: don't allocate a buffer for console print on\n\tstack","Message-ID":"<20170317050930.GB28075@kroah.com>","References":"<1487364165-21882-1-git-send-email-jan.dakinevich@gmail.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"<1487364165-21882-1-git-send-email-jan.dakinevich@gmail.com>","User-Agent":"Mutt/1.8.0 (2017-02-23)","X-BeenThere":"linuxppc-dev@lists.ozlabs.org","X-Mailman-Version":"2.1.23","Precedence":"list","List-Id":"Linux on PowerPC Developers Mail List\n\t","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Cc":"Peter Hurley , Arnd Bergmann , \n\tAmit Shah , linux-kernel@vger.kernel.org,\n\tvirtualization@lists.linux-foundation.org, Jiri Slaby , \n\tlinuxppc-dev@lists.ozlabs.org, Dan Carpenter ","Errors-To":"linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org","Sender":"\"Linuxppc-dev\"\n\t"}},{"id":1612109,"web_url":"http://patchwork.ozlabs.org/comment/1612109/","msgid":"<18f113d4-9c37-0114-d637-3720ad093722@gmail.com>","date":"2017-03-20T15:55:15","subject":"Re: [PATCH] tty: hvc: don't allocate a buffer for console print on\n\tstack","submitter":{"id":71018,"url":"http://patchwork.ozlabs.org/api/people/71018/","name":"Jan Dakinevich","email":"jan.dakinevich@gmail.com"},"content":"> You shouldn't use 'static' data either, that's not always guaranteed to\n> be DMA-able, right?\n\nI naively thought all 'static' data was linked into .data and the\nsection was always kmapped.\n\n> What about allocating it dynamically? That's the correct thing to do.\n\nYep, the solution was more welcomed and happened earlier:\nhttps://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c4baad50297d84bde1a7ad45e50c73adae4a2192\n\nOn 03/17/2017 08:09 AM, Greg Kroah-Hartman wrote:\n> On Fri, Feb 17, 2017 at 11:42:45PM +0300, Jan Dakinevich wrote:\n>> The buffer is used by virtio console driver as DMA buffer. Since v4.9\n>> (if VMAP_STACK is enabled) we shouldn't use the stack for DMA.\n> \n> You shouldn't use 'static' data either, that's not always guaranteed to\n> be DMA-able, right?\n> \n>>\n>> Signed-off-by: Jan Dakinevich \n>> ---\n>> drivers/tty/hvc/hvc_console.c | 7 ++++++-\n>> 1 file changed, 6 insertions(+), 1 deletion(-)\n>>\n>> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c\n>> index 9b5c0fb..1ce6aaf 100644\n>> --- a/drivers/tty/hvc/hvc_console.c\n>> +++ b/drivers/tty/hvc/hvc_console.c\n>> @@ -143,10 +143,15 @@ static struct hvc_struct *hvc_get_by_index(int index)\n>> static void hvc_console_print(struct console *co, const char *b,\n>> \t\t\t unsigned count)\n>> {\n>> -\tchar c[N_OUTBUF] __ALIGNED__;\n>> \tunsigned i = 0, n = 0;\n>> \tint r, donecr = 0, index = co->index;\n>> \n>> +\t/*\n>> +\t * Access to the buffer is serialized by console_sem in caller code from\n>> +\t * kernel/printk/printk.c\n>> +\t */\n>> +\tstatic char c[N_OUTBUF] __ALIGNED__;\n> \n> What about allocating it dynamically? That's the correct thing to do.\n> \n> thanks,\n> \n> greg k-h\n>","headers":{"Return-Path":"","X-Original-To":["patchwork-incoming@ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":["patchwork-incoming@ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Received":["from lists.ozlabs.org (lists.ozlabs.org [103.22.144.68])\n\t(using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3vn0vW0mXdz9s3w\n\tfor ;\n\tTue, 21 Mar 2017 02:57:27 +1100 (AEDT)","from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3])\n\tby lists.ozlabs.org (Postfix) with ESMTP id 3vn0vV6mpJzDqcD\n\tfor ;\n\tTue, 21 Mar 2017 02:57:26 +1100 (AEDT)","from mail-lf0-x241.google.com (mail-lf0-x241.google.com\n\t[IPv6:2a00:1450:4010:c07::241])\n\t(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128\n\tbits)) (No client certificate requested)\n\tby lists.ozlabs.org (Postfix) with ESMTPS id 3vn0rP0DDpzDq5g\n\tfor ;\n\tTue, 21 Mar 2017 02:54:45 +1100 (AEDT)","by mail-lf0-x241.google.com with SMTP id r36so10695071lfi.0\n\tfor ;\n\tMon, 20 Mar 2017 08:54:44 -0700 (PDT)","from [127.0.0.1] (host5.infotecs.ru. 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