kcsan, trace: Make KCSAN compatible with tracing (f5d2313b) · Commits · 戴 / test

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. Furthermore, since KCSAN relies on udelay() to introduce delay, we have to disable ftrace for udelay() (currently done for x86) in case KCSAN is used together with lockdep and ftrace. The reason is that it may corrupt lockdep IRQ flags tracing state due to a peculiar case of recursion (details in Makefile comment). Reported-by:

Qian Cai <cai@lca.pw> Tested-by:

Qian Cai <cai@lca.pw> Acked-by:

Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by:

Marco Elver <elver@google.com> Signed-off-by:

Paul E. McKenney <paulmck@kernel.org> Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/lib/Makefile

+5 −0

Original line number	Diff line number	Diff line
		@@ -8,6 +8,11 @@ KCOV_INSTRUMENT_delay.o := n

		# KCSAN uses udelay for introducing watchpoint delay; avoid recursion.
		KCSAN_SANITIZE_delay.o := n
		ifdef CONFIG_KCSAN
		# In case KCSAN+lockdep+ftrace are enabled, disable ftrace for delay.o to avoid
		# lockdep -> [other libs] -> KCSAN -> udelay -> ftrace -> lockdep recursion.
		CFLAGS_REMOVE_delay.o = $(CC_FLAGS_FTRACE)
		endif

		# Early boot use of cmdline; don't instrument it
		ifdef CONFIG_AMD_MEM_ENCRYPT

kernel/kcsan/Makefile

+2 −0

Original line number	Diff line number	Diff line
		@@ -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,)

kernel/trace/Makefile

+3 −0

Original line number	Diff line number	Diff line
		@@ -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)

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