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From: David Miller on 18 Mar 2010 02:30
From: Frederic Weisbecker <fweisbec(a)gmail.com>
Date: Thu, 18 Mar 2010 05:49:33 +0100

> While using the lock events through perf in a sparc box, I can see
> the following message repeated many times:
>
> Kernel unaligned access at TPC[49357c] perf_trace_lock_acquire+0xb4/0x180
>
> It actually hangs the box as the messages are sent to a serial console.
>
> When used with perf, the trace events use a per cpu buffer allocated
> in kernel/trace/trace_event_perf.c, and the allocation appears to return
> a misaligned percpu pointer. It is aligned to 4 while it seems it
> requires to be aligned to 8.

Thanks I'll take a look at this.

RAW locks (both rwlocks and spinlocks) on sparc64 are 4-bytes
in size, maybe some piece of code is assuming that locks
are cpu word sized.

Where is perf_trace_lock_acquire() I can't find it in Linus's
tree? Does it get created by some crazy macro expansion?

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From: David Miller on 18 Mar 2010 02:30

I can't even find kernel/trace/trace_event_perf.c, what tree
are you using?
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From: Li Zefan on 18 Mar 2010 02:40
David Miller wrote:
> From: Frederic Weisbecker <fweisbec(a)gmail.com>
> Date: Thu, 18 Mar 2010 05:49:33 +0100
>
>> While using the lock events through perf in a sparc box, I can see
>> the following message repeated many times:
>>
>> Kernel unaligned access at TPC[49357c] perf_trace_lock_acquire+0xb4/0x180
>>
>> It actually hangs the box as the messages are sent to a serial console.
>>
>> When used with perf, the trace events use a per cpu buffer allocated
>> in kernel/trace/trace_event_perf.c, and the allocation appears to return
>> a misaligned percpu pointer. It is aligned to 4 while it seems it
>> requires to be aligned to 8.
>
> Thanks I'll take a look at this.
>
> RAW locks (both rwlocks and spinlocks) on sparc64 are 4-bytes
> in size, maybe some piece of code is assuming that locks
> are cpu word sized.
>
> Where is perf_trace_lock_acquire() I can't find it in Linus's
> tree? Does it get created by some crazy macro expansion?
>

Yes, it's expanded by some crazy macro in include/trace/ftrace.h..

In linus' tree, it's called ftrace_profile_lock_acquire(), and it's
renamed to perf_trace_lock_acquire() in -tip tree by commit
97d5a22005f38057b4bc0d95f81cd26510268794.

#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
static notrace void \
ftrace_profile_templ_##call(struct ftrace_event_call *event_call, \
proto) \
{ \
struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
struct ftrace_raw_##call *entry; \
u64 __addr = 0, __count = 1; \
unsigned long irq_flags; \
int __entry_size; \
int __data_size; \
int rctx; \
\
....
}
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From: Li Zefan on 18 Mar 2010 02:40
David Miller wrote:
> I can't even find kernel/trace/trace_event_perf.c, what tree

It's kernel/trace/trace_event_profile.c in linus' tree.

> are you using?

must be Ingo's -tip tree, or his own tree which is based on -tip tree.
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From: Tejun Heo on 18 Mar 2010 05:40
Hello,

On 03/18/2010 01:49 PM, Frederic Weisbecker wrote:
> Hi,
>
> While using the lock events through perf in a sparc box, I can see
> the following message repeated many times:
>
> Kernel unaligned access at TPC[49357c] perf_trace_lock_acquire+0xb4/0x180
>
> It actually hangs the box as the messages are sent to a serial console.
>
> When used with perf, the trace events use a per cpu buffer allocated
> in kernel/trace/trace_event_perf.c, and the allocation appears to return
> a misaligned percpu pointer. It is aligned to 4 while it seems it
> requires to be aligned to 8.

Does this fix the problem?

diff --git a/kernel/trace/trace_event_profile.c b/kernel/trace/trace_event_profile.c
index c1cc3ab..d3f7d1b 100644
--- a/kernel/trace/trace_event_profile.c
+++ b/kernel/trace/trace_event_profile.c
@@ -27,13 +27,15 @@ static int ftrace_profile_enable_event(struct ftrace_event_call *event)
return 0;

if (!total_profile_count) {
- buf = (char *)alloc_percpu(perf_trace_t);
+ buf = (char *)__alloc_percpu(sizeof(perf_trace_t),
+ __alignof__(unsigned long));
if (!buf)
goto fail_buf;

rcu_assign_pointer(perf_trace_buf, buf);

- buf = (char *)alloc_percpu(perf_trace_t);
+ buf = (char *)__alloc_percpu(sizeof(perf_trace_t),
+ __alignof__(unsigned long));
if (!buf)
goto fail_buf_nmi;



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tejun
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