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Date: Mon, 17 Feb 2020 15:14:49 -0800 From: "Paul E. McKenney" <paulmck@...nel.org> To: Qian Cai <cai@....pw> Cc: Marco Elver <elver@...gle.com>, andreyknvl@...gle.com, glider@...gle.com, dvyukov@...gle.com, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, rostedt@...dmis.org, mingo@...hat.com, x86@...nel.org Subject: Re: [PATCH v2] kcsan, trace: Make KCSAN compatible with tracing On Mon, Feb 17, 2020 at 12:06:14PM -0500, Qian Cai wrote: > On Fri, 2020-02-14 at 15:40 -0800, Paul E. McKenney wrote: > > On Fri, Feb 14, 2020 at 10:10:35PM +0100, Marco Elver wrote: > > > 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@...gle.com> > > > Reported-by: Qian Cai <cai@....pw> > > > Cc: Paul E. McKenney <paulmck@...nel.org> > > > Cc: Steven Rostedt <rostedt@...dmis.org> > > > > Queued for review and further testing, thank you! > > > > Qian, does this also fix things for you? > > It works fine. Feel free to use, > > Tested-by: Qian Cai <cai@....pw> Applied, thank you! Thanx, Paul > > > --- > > > v2: > > > * Fix KCSAN+lockdep+ftrace compatibility. > > > --- > > > 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 432a077056775..6110bce7237bd 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 df6b7799e4927..d4999b38d1be5 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 f9dcd19165fa2..6b601d88bf71e 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) > > > -- > > > 2.25.0.265.gbab2e86ba0-goog > > >
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