Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756719AbYHTNOU (ORCPT ); Wed, 20 Aug 2008 09:14:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753243AbYHTNOM (ORCPT ); Wed, 20 Aug 2008 09:14:12 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:62199 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753164AbYHTNOL (ORCPT ); Wed, 20 Aug 2008 09:14:11 -0400 Date: Wed, 20 Aug 2008 09:14:09 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Benjamin Herrenschmidt cc: "Paul E. McKenney" , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Steven Rostedt , Scott Wood , Eran Liberty , Alan Modra , Segher Boessenkool Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3) In-Reply-To: <1219216705.21386.46.camel@pasglop> Message-ID: References: <48591941.4070408@extricom.com> <48A92E15.2080709@extricom.com> <48A9901B.1080900@redhat.com> <20080818154746.GA26835@Krystal> <48A9AFA7.8080508@freescale.com> <1219110814.8062.2.camel@pasglop> <1219113549.8062.13.camel@pasglop> <1219114600.8062.15.camel@pasglop> <1219119431.8062.35.camel@pasglop> <1219216705.21386.46.camel@pasglop> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1316 Lines: 35 On Wed, 20 Aug 2008, Benjamin Herrenschmidt wrote: > Found the problem (or at least -a- problem), it's a gcc bug. > > Well, first I must say the code generated by -pg is just plain > horrible :-) > > Appart from that, look at the exit of, for example, __d_lookup, as > generated by gcc when ftrace is enabled: > > c00c0498: 38 60 00 00 li r3,0 > c00c049c: 81 61 00 00 lwz r11,0(r1) > c00c04a0: 80 0b 00 04 lwz r0,4(r11) > c00c04a4: 7d 61 5b 78 mr r1,r11 > c00c04a8: bb 0b ff e0 lmw r24,-32(r11) > c00c04ac: 7c 08 03 a6 mtlr r0 > c00c04b0: 4e 80 00 20 blr > > As you can see, it restores r1 -before- it pops r24..r31 off > the stack ! I let you imagine what happens if an interrupt happens > just in between those two instructions (mr and lmw). We don't do > redzones on our ABI, so basically, the registers end up corrupted > by the interrupt. Ouch! You've disassembled this without -pg too, and it does not have this bug? What version of gcc do you have? -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/