Messages in this thread | | | Date | Tue, 06 Oct 2009 15:30:40 -0700 | From | "Justin P. Mattock" <> | Subject | Re: system gets stuck in a lock during boot |
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Jason Baron wrote: > On Mon, Oct 05, 2009 at 09:24:09PM -0400, Steven Rostedt wrote: > >> On Fri, 2009-10-02 at 17:12 -0400, Jason Baron wrote: >> >> >>> hi Justin, >>> >>> I've been playing around with gcc '4.5' as well and hit a panic that >>> looks very similar to what you've seen with stock 2.6.31 - I haven't >>> seen it anywhere else. Anyways, it seems to be some sort of alignment >>> issue with the 'struct ftrace_event_call'. I'm not sure yet if this is a >>> compiler or kernel issue. But the following kernel patch fixes the issue >>> for me. It would be interesting to verify if the patch also resolves the >>> issue for you. >>> >>> thanks, >>> >>> -Jason >>> >>> >>> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h >>> index 6ad76bf..0029af4 100644 >>> --- a/include/asm-generic/vmlinux.lds.h >>> +++ b/include/asm-generic/vmlinux.lds.h >>> @@ -164,6 +164,7 @@ >>> LIKELY_PROFILE() \ >>> BRANCH_PROFILE() \ >>> TRACE_PRINTKS() \ >>> + . = ALIGN(32); \ >>> FTRACE_EVENTS() \ >>> TRACE_SYSCALLS() >>> >>> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h >>> index a81170d..43f9f1e 100644 >>> --- a/include/linux/ftrace_event.h >>> +++ b/include/linux/ftrace_event.h >>> @@ -124,7 +124,7 @@ struct ftrace_event_call { >>> atomic_t profile_count; >>> int (*profile_enable)(struct ftrace_event_call *); >>> void (*profile_disable)(struct ftrace_event_call *); >>> -}; >>> +} __attribute__((aligned(32))); >>> >>> #define MAX_FILTER_PRED 32 >>> #define MAX_FILTER_STR_VAL 128 >>> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h >>> index f64fbaa..4697fb6 100644 >>> --- a/include/trace/ftrace.h >>> +++ b/include/trace/ftrace.h >>> @@ -600,7 +600,7 @@ static int ftrace_raw_init_event_##call(void) \ >>> } \ >>> \ >>> static struct ftrace_event_call __used \ >>> -__attribute__((__aligned__(4))) \ >>> +__attribute__((__aligned__(32))) \ >>> __attribute__((section("_ftrace_events"))) event_##call = { \ >>> .name = #call, \ >>> .system = __stringify(TRACE_SYSTEM), \ >>> >> Are all alignments needed? Or just adding one might help. Or removing >> the one directly above? >> >> -- Steve >> >> > > 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<jbaron@redhat.com> > > > 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 */ > > #define MAX_FILTER_PRED 32 > #define MAX_FILTER_STR_VAL 128 > diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h > index f64fbaa..e344e81 100644 > --- a/include/trace/ftrace.h > +++ b/include/trace/ftrace.h > @@ -600,7 +600,6 @@ 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), \ > > > > > shoot I don't know why this is still hitting. tried both patches and still. As of now the only thing I can think of besides looking at kernel/compiler is the patch for sysvinit to load the policy(maybe something in there is old/outdated).
(BTW: not sure if it means anything but this system is x86_64 built from the multilib clfs, but with no 32 bit libs, pretty much how fedora11 has there system built)
Justin P. Mattock
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