Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751859AbZJGCm6 (ORCPT ); Tue, 6 Oct 2009 22:42:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751035AbZJGCm5 (ORCPT ); Tue, 6 Oct 2009 22:42:57 -0400 Received: from mail-ew0-f217.google.com ([209.85.219.217]:39864 "EHLO mail-ew0-f217.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750845AbZJGCm5 (ORCPT ); Tue, 6 Oct 2009 22:42:57 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; b=j+MUo0VjETg7FEEfuEKEhDHeQAVXiRQk4ubL0MFG0m6cdXyvXQ9VX0OatkjR2TrCBQ JGDjlqtpzb5JjXRasZxiueF0C9gTqLCHof0mmRsH5Dr3QQYyjwOWZrjtFm4eGtDupnLW 1iwa0mQ6t2Frvv6ULZ1Pw1F2N1z1PMZXOJlPA= Message-ID: <4ACC001D.4050105@gmail.com> Date: Tue, 06 Oct 2009 19:42:37 -0700 From: "Justin P. Mattock" User-Agent: Spicebird/0.7.1 (X11; 2009022519) MIME-Version: 1.0 To: rostedt@goodmis.org CC: Jason Baron , Ingo Molnar , Peter Zijlstra , Li Zefan , Frederic Weisbecker , Linux Kernel Mailing List Subject: Re: system gets stuck in a lock during boot References: <1251096925.7538.121.camel@twins> <4A9251EB.8040805@gmail.com> <20090825085919.GB14003@elte.hu> <4A94803A.5060408@gmail.com> <20090826073351.GE23435@elte.hu> <4A9549E5.5020002@gmail.com> <20091002211211.GA2633@redhat.com> <1254792249.13160.213.camel@gandalf.stny.rr.com> <20091006203225.GC2631@redhat.com> <1254880921.1696.112.camel@gandalf.stny.rr.com> In-Reply-To: <1254880921.1696.112.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4134 Lines: 109 Steven Rostedt wrote: > On Tue, 2009-10-06 at 16:32 -0400, Jason Baron wrote: > > >> So the problem I'm seeing is an oops on boot caused by the call->system pointer >> deference in event_create_dir(). The 'call' variable is of type 'struct >> ftrace_event_call'. >> >> What's going on is that the 'struct ftrace_event_call' is of size 168 bytes >> (sizeof(struct ftrace_event_call)) = 168 = 0xA8. However, in memory the >> structures are 16-byte aligned. Thus, the stride for walking through the >> pointers needs to be 176 (0xB0), but instead its 168 causing the oops. >> >> I've only seen this issue while using gcc (GCC) 4.5.0 20090916, on a >> vanilla 2.6.31 kernel. >> >> That said, I'm not sure the compiler is doing the wrong thing here. The >> 'struct ftrace_event_call' contains an embedded 'struct list_head' which >> is 16 bytes. According to the gcc docs, the aligned attribute, 'specifies a >> minimum alignment for the variable or structure field, measured in bytes'. >> Thus, at least according to the docs, gcc can increase the alignment of the >> 'struct ftrace_event_call', from its original specification of 4, to 16. Even >> in the case where we are working corectly the structures are 8-byte aligned. >> >> Thus, I would reccommend the patch below as a preventive measure. Its >> the minimal patch I've found to resolve this issue. In general, if we >> are going to walk data structures embedded in a special elf section, I >> think the general rules needs to be to set the alignment to the power of >> two which is greater than or equal to the largest item in the structure. >> >> thanks, >> >> -Jason >> >> Signed-off-by: Jason Baron >> >> >> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h >> index a81170d..7182f03 100644 >> --- a/include/linux/ftrace_event.h >> +++ b/include/linux/ftrace_event.h >> @@ -124,7 +124,10 @@ struct ftrace_event_call { >> atomic_t profile_count; >> int (*profile_enable)(struct ftrace_event_call *); >> void (*profile_disable)(struct ftrace_event_call *); >> -}; >> +} __attribute__((aligned(16))); >> + >> +/* Align to the largest field in the data structure: >> + * sizeof(struct list_head) = 16 */ >> > > Is this true for i386? > > I just tried this patch and it seems to work. Can you give it a try. > > Signed-off-by: Steven Rostedt > > > diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h > index 4ec5e67..044b70d 100644 > --- a/include/linux/ftrace_event.h > +++ b/include/linux/ftrace_event.h > @@ -133,7 +133,7 @@ struct ftrace_event_call { > atomic_t profile_count; > int (*profile_enable)(void); > void (*profile_disable)(void); > -}; > +} __attribute__((aligned(sizeof(struct list_head)))); > > #define FTRACE_MAX_PROFILE_SIZE 2048 > > diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h > index cc0d966..31e7637 100644 > --- a/include/trace/ftrace.h > +++ b/include/trace/ftrace.h > @@ -501,7 +501,6 @@ static void ftrace_profile_disable_##call(void) \ > * } > * > * static struct ftrace_event_call __used > - * __attribute__((__aligned__(4))) > * __attribute__((section("_ftrace_events"))) event_ = { > * .name = "", > * .system = "", > @@ -619,7 +618,6 @@ static int ftrace_raw_init_event_##call(void) \ > } \ > \ > static struct ftrace_event_call __used \ > -__attribute__((__aligned__(4))) \ > __attribute__((section("_ftrace_events"))) event_##call = { \ > .name = #call, \ > .system = __stringify(TRACE_SYSTEM), \ > > > > o.k. applied your patch, but unfortunantly I still am hitting this kernel panic. must admit I have no idea why this is doing this. (but am willing to sit through this, because eventually sooner or later will hit this if I update gcc). Justin P. Mattock -- 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/