Re: [BUG] percpu misaligned allocation

[Tejun Heo <tj@kernel.org>]

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;
 


-- 
tejun