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 4DFD8C433EF for ; Fri, 20 May 2022 08:03:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235920AbiETIDh convert rfc822-to-8bit (ORCPT ); Fri, 20 May 2022 04:03:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229564AbiETIDf (ORCPT ); Fri, 20 May 2022 04:03:35 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 7E0206898F for ; Fri, 20 May 2022 01:03:32 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-231-j6MuEwWEOMq97IGnC72OWw-1; Fri, 20 May 2022 09:03:30 +0100 X-MC-Unique: j6MuEwWEOMq97IGnC72OWw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.36; Fri, 20 May 2022 09:03:29 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.036; Fri, 20 May 2022 09:03:29 +0100 From: David Laight To: 'Matthew Wilcox' CC: 'Kent Overstreet' , "linux-kernel@vger.kernel.org" , "linux-mm@vger.kernel.org" , "pmladek@suse.com" , "rostedt@goodmis.org" , "senozhatsky@chromium.org" , "andriy.shevchenko@linux.intel.com" Subject: RE: [PATCH v2 03/28] vsprintf: %pf(%p) Thread-Topic: [PATCH v2 03/28] vsprintf: %pf(%p) Thread-Index: AQHYa6VkVQCoxy629k+LRSm5RxWDEq0mrmAQ///0sICAAMIK4A== Date: Fri, 20 May 2022 08:03:29 +0000 Message-ID: <786516a0b71a4c6689592b89b146edec@AcuMS.aculab.com> References: <20220519172421.162394-1-kent.overstreet@gmail.com> <20220519172421.162394-4-kent.overstreet@gmail.com> <141b17a257274fc38291cdb07e0e23b6@AcuMS.aculab.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthew Wilcox > Sent: 19 May 2022 22:15 > > On Thu, May 19, 2022 at 09:06:24PM +0000, David Laight wrote: > > I suspect this a very good way to blow the kernel stack. > > The highest stack use is already very likely to be inside > > the printf code in an error path somewhere. > > ... > > > Double copying using a temporary buffer isn't the end of the world. > > How can you hold both of these positions simultaneously? Mostly you only need a short(ish) buffer to format a single item. But even a full line buffer is probably less stack than a nested printf call. It certainly makes it possible for static analysis to determine maximum stack depth. That made me realise that one of the problems doing static analysis of stack depth is indirect calls. The hashes that (IIRC) fine-ibt add to indirect calls and functions make it possible to tie these together. So you can determine the worst one of the called functions and use it for the stack depth at the call sites. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)