linux-kernel - [RFC PATCH 5/6] powerpc/stacktrace: Include ftraced function in arch_stack_walk

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Date:   Fri, 21 May 2021 12:18:40 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Suchanek <msuchanek@...e.de>,
        Torsten Duwe <duwe@...e.de>
Cc:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 5/6] powerpc/stacktrace: Include ftraced function in arch_stack_walk_reliable()

With -mprofile-kernel and ppc32, the function tracer is invoked before a
function sets up its own stackframe. This results in the traced function
not appearing in stack traces. Fix this by checking for ftrace entry and
including the traced function in the stack trace.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
While I don't think we expect to see ftrace show up in the trace for a 
non-running task, I think it is good to cover this scenario. I also 
think it is ok to consider such traces to be reliable. But, I'm not sure 
of the implications w.r.t livepatching.

- Naveen


 arch/powerpc/kernel/stacktrace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 1deb1bf331ddbd..1e1be297c5d6c7 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -160,6 +160,10 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 
 		if (!consume_entry(cookie, ip))
 			return -EINVAL;
+
+		ip = ftrace_get_traced_func_if_no_stackframe(ip, stack);
+		if (ip && !consume_entry(cookie, ip))
+			return -EINVAL;
 	}
 	return 0;
 }
-- 
2.30.2