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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.

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>
This commit is contained in:
Marco Elver 2020-02-14 22:10:35 +01:00 committed by Ingo Molnar
parent 703b321501
commit f5d2313bd3
3 changed files with 10 additions and 0 deletions
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5
arch/x86/lib/Makefile
View file

@ -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

2
kernel/kcsan/Makefile
View file

@ -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,)

3
kernel/trace/Makefile
View file

@ -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)