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Subject[PATCH] kcsan, trace: Make KCSAN compatible with tracing
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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@google.com>
Reported-by: Qian Cai <cai@lca.pw>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.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
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