Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933764AbZJGCEB (ORCPT ); Tue, 6 Oct 2009 22:04:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756903AbZJGCEB (ORCPT ); Tue, 6 Oct 2009 22:04:01 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:53970 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754043AbZJGCEA (ORCPT ); Tue, 6 Oct 2009 22:04:00 -0400 Subject: Re: system gets stuck in a lock during boot From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Jason Baron Cc: Justin Mattock , Ingo Molnar , Peter Zijlstra , Li Zefan , Frederic Weisbecker , Linux Kernel Mailing List In-Reply-To: <20091006203225.GC2631@redhat.com> 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> Content-Type: text/plain Organization: Kihon Technologies Inc. Date: Tue, 06 Oct 2009 22:02:01 -0400 Message-Id: <1254880921.1696.112.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3702 Lines: 96 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), \ -- 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/