From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: alignment faults in 3.6 Date: Fri, 12 Oct 2012 12:07:50 +0100 Message-ID: <20121012110750.GE21164@n2100.arm.linux.org.uk> References: <20121005082439.GF4625@n2100.arm.linux.org.uk> <201210120811.43290.arnd@arndb.de> <20121012090321.GA21164@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Arnd Bergmann , linux-arm-kernel@lists.infradead.org, David Laight , Eric Dumazet , netdev@vger.kernel.org, Jon Masters To: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= Return-path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:51029 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751598Ab2JLLII (ORCPT ); Fri, 12 Oct 2012 07:08:08 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Fri, Oct 12, 2012 at 12:00:03PM +0100, M=E5ns Rullg=E5rd wrote: > Russell King - ARM Linux writes: >=20 > > On Fri, Oct 12, 2012 at 08:11:42AM +0000, Arnd Bergmann wrote: > >> On Thursday 11 October 2012, M=E5ns Rullg=E5rd wrote: > >> > > But, the IP header is expected to be aligned. > >> >=20 > >> > Everything tells the compiler the struct is perfectly aligned. = When the > >> > buggy driver passes a misaligned pointer, bad things happen. > >>=20 > >> Would it be appropriate to add a WARN_ON_ONCE() in the alignment f= ault path > >> then? >=20 > I think that's an excellent idea. Well, I get the last word here and it's no. > >> If all alignment faults in the kernel are caused by broken drivers= , > >> that would at least give us some hope of finding those drivers whi= le > >> at the same time not causing much overhead in the case where we ne= ed > >> to do the fixup in the meantime. > > > > No. It is my understanding that various IP option processing can a= lso > > cause the alignment fault handler to be invoked, even when the pack= et is > > properly aligned, and then there's jffs2/mtd which also relies upon > > alignment faults being fixed up. >=20 > As far as I'm concerned, this is all hearsay, and I've only ever hear= d > it from you. Why can't you let those who care fix these bugs instead= ? You know, I'm giving you the benefit of my _knowledge_ which has been built over the course of the last 20 years. I've been in these discussions with networking people before. I ended up having to develo= p the alignment fault handler because of those discussions. And oh look, Eric confirmed that the networking code isn't going to get "fixed" as you were demanding, which is exactly what I said. I've been in discussions with MTD people over these issues before, I've discussed this with David Woodhouse when it came up in JFFS2. I *KNOW* these things. You can call it hearsay if you wish, but it seems to be more accurate than your wild outlandish and pathetic statements.