linux-kernel - [PATCH] kcsan, trace: Make KCSAN compatible with tracing

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Date:   Fri, 14 Feb 2020 20:05:00 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com
Cc:     paulmck@...nel.org, andreyknvl@...gle.com, glider@...gle.com,
        dvyukov@...gle.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        mingo@...hat.com, Qian Cai <cai@....pw>
Subject: [PATCH] kcsan, trace: Make KCSAN compatible with tracing

Previously the system would lock up if ftrace was enabled together with
KCSAN. This is due to recursion on reporting if the tracer code is
instrumented with KCSAN.

To avoid this for all types of tracing, disable KCSAN instrumentation
for all of kernel/trace.

Signed-off-by: Marco Elver <elver@...gle.com>
Reported-by: Qian Cai <cai@....pw>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/kcsan/Makefile | 2 ++
 kernel/trace/Makefile | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index df6b7799e4927..d4999b38d1be5 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -4,6 +4,8 @@ KCOV_INSTRUMENT := n
 UBSAN_SANITIZE := n
 
 CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
 CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
 	$(call cc-option,-fno-stack-protector,)
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index f9dcd19165fa2..6b601d88bf71e 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -6,6 +6,9 @@ ifdef CONFIG_FUNCTION_TRACER
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
 KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
 
+# Avoid recursion due to instrumentation.
+KCSAN_SANITIZE := n
+
 ifdef CONFIG_FTRACE_SELFTEST
 # selftest needs instrumentation
 CFLAGS_trace_selftest_dynamic.o = $(CC_FLAGS_FTRACE)
-- 
2.25.0.265.gbab2e86ba0-goog