Re: [PATCH] tracing/trace_stack: Fix stack trace on ppc64

From: Steven Rostedt
Date: Tue Aug 31 2010 - 10:58:48 EST


On Tue, 2010-08-31 at 16:21 +0200, Frederic Weisbecker wrote:
> On Mon, Aug 30, 2010 at 09:31:50PM -0400, Steven Rostedt wrote:
> > On Wed, 2010-08-25 at 11:32 +1000, Anton Blanchard wrote:
> > > save_stack_trace() stores the instruction pointer, not the function
> > > descriptor. On ppc64 the trace stack code currently dereferences the
> > > instruction pointer and shows 8 bytes of instructions in our backtraces:
> > >
> > > # cat /sys/kernel/debug/tracing/stack_trace
> > > Depth Size Location (26 entries)
> > > ----- ---- --------
> > > 0) 5424 112 0x6000000048000004
> > > 1) 5312 160 0x60000000ebad01b0
> > > 2) 5152 160 0x2c23000041c20030
> > > 3) 4992 240 0x600000007c781b79
> > > 4) 4752 160 0xe84100284800000c
> > > 5) 4592 192 0x600000002fa30000
> > > 6) 4400 256 0x7f1800347b7407e0
> > > 7) 4144 208 0xe89f0108f87f0070
> > > 8) 3936 272 0xe84100282fa30000
> > >
> > > Since we aren't dealing with function descriptors, use %pS instead of %pF
> > > to fix it:
> > >
> > > # cat /sys/kernel/debug/tracing/stack_trace
> > > Depth Size Location (26 entries)
> > > ----- ---- --------
> > > 0) 5424 112 ftrace_call+0x4/0x8
> > > 1) 5312 160 .current_io_context+0x28/0x74
> > > 2) 5152 160 .get_io_context+0x48/0xa0
> > > 3) 4992 240 .cfq_set_request+0x94/0x4c4
> > > 4) 4752 160 .elv_set_request+0x60/0x84
> > > 5) 4592 192 .get_request+0x2d4/0x468
> > > 6) 4400 256 .get_request_wait+0x7c/0x258
> > > 7) 4144 208 .__make_request+0x49c/0x610
> > > 8) 3936 272 .generic_make_request+0x390/0x434
> > >
> > > Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>
> >
> > Thanks, I'll test this to make sure it doesn't break x86, and then push
> > it into a stable/-rc patch queue.
> >
> > -- Steve
>
>
> Ingo has applied it already in perf/urgent.

Hmm, I never saw the tip-bot reply :-(

I guess it only sends to the Cc tags.

-- Steve


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