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authorMarco Elver <elver@google.com>2020-02-15 00:10:35 +0300
committerIngo Molnar <mingo@kernel.org>2020-03-21 11:44:41 +0300
commitf5d2313bd3c540be405c4977a63840cd6d0167b5 (patch)
tree25a8bfd1f857fc11aab179fb67ac36071e9c1503
parent703b321501c95c658275fd76775282fe45989641 (diff)
downloadlinux-f5d2313bd3c540be405c4977a63840cd6d0167b5.tar.xz
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. 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>
-rw-r--r--arch/x86/lib/Makefile5
-rw-r--r--kernel/kcsan/Makefile2
-rw-r--r--kernel/trace/Makefile3
3 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 432a07705677..6110bce7237b 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -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
diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index df6b7799e492..d4999b38d1be 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 f9dcd19165fa..6b601d88bf71 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)