Messages in this thread | | | Date | Mon, 9 Mar 2020 13:27:14 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH kcsan 26/32] kcsan, trace: Make KCSAN compatible with tracing |
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On Mon, Mar 09, 2020 at 03:57:22PM -0400, Steven Rostedt wrote: > 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>
Applied, thank you!
Thanx, Paul
> -- 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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