linux-kernel - powerpc ftrace broken due to "manual merge of the ftrace tree with the arm64 tree"

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Date:   Fri, 15 Nov 2019 15:28:52 -0500
From:   Qian Cai <cai@....pw>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: powerpc ftrace broken due to "manual merge of the ftrace tree with
 the arm64 tree"

# echo function >/sys/kernel/debug/tracing/current_tracer

It hangs forever with today's linux-next on powerpc. Reverted the conflict fix
[1] as below fixes the issue.

[1] https://lore.kernel.org/linux-next/20191115135357.10386fac@canb.auug.org.au/

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-
generic/vmlinux.lds.h
index 7d0d03a03d4d..a92222f79b53 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -136,29 +136,20 @@
 #endif
 
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
-/*
- * The ftrace call sites are logged to a section whose name depends on the
- * compiler option used. A given kernel image will only use one, AKA
- * FTRACE_CALLSITE_SECTION. We capture all of them here to avoid header
- * dependencies for FTRACE_CALLSITE_SECTION's definition.
- */
-/*
- * Need to also make ftrace_graph_stub point to ftrace_stub
- * so that the same stub location may have different protocols
- * and not mess up with C verifiers.
- */
-#define MCOUNT_REC()	. = ALIGN(8);				\
+#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
+#define MCOUNT_REC()	. = ALIGN(8)				\
 			__start_mcount_loc = .;			\
-			KEEP(*(__mcount_loc))			\
 			KEEP(*(__patchable_function_entries))	\
 			__stop_mcount_loc = .;			\
 			ftrace_graph_stub = ftrace_stub;
 #else
-# ifdef CONFIG_FUNCTION_TRACER
-#  define MCOUNT_REC()	ftrace_graph_stub = ftrace_stub;
-# else
-#  define MCOUNT_REC()
-# endif
+#define MCOUNT_REC()	. = ALIGN(8);				\
+			__start_mcount_loc = .;			\
+			KEEP(*(__mcount_loc))			\
+			__stop_mcount_loc = .;
+#endif
+#else
+#define MCOUNT_REC()
 #endif
 
 #ifdef CONFIG_TRACE_BRANCH_PROFILING