Messages in this thread | | | Date | Mon, 9 Mar 2020 15:57:22 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH kcsan 26/32] kcsan, trace: Make KCSAN compatible with tracing |
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On Mon, 9 Mar 2020 12:04:14 -0700 paulmck@kernel.org wrote:
> From: Marco Elver <elver@google.com> > > 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). > > 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>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > Tested-by: Qian Cai <cai@lca.pw> > --- > arch/x86/lib/Makefile | 5 +++++ > kernel/kcsan/Makefile | 2 ++ > kernel/trace/Makefile | 3 +++ > 3 files changed, 10 insertions(+) > > diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile > index 432a077..6110bce7 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 df6b779..d4999b3 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 0e63db6..9072486 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)
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