On Wed, 13 May 2020 at 13:11, Peter Zijlstra <[email protected]> wrote: > > On Tue, May 12, 2020 at 10:31:44PM +0200, Marco Elver wrote: > > On Tue, 12 May 2020 at 21:08, Peter Zijlstra <[email protected]> wrote: > > > > data_race() will include active calls to kcsan_{dis,en}able_current(), > > > and this must not happen. > > > > Only if instrumentation is enabled for the compilation unit. If you > > have KCSAN_SANITIZE_foo.c := n, no calls are emitted not even to > > kcsan_{dis,en}able_current(). Does that help? > > > > By default, right now __READ_ONCE() will still generate a call due to > > instrumentation (call to __tsan_readX). > > Ah, so looking at: > > #define data_race(expr) \ > ({ \ > __kcsan_disable_current(); \ > ({ \ > __unqual_scalar_typeof(({ expr; })) __v = ({ expr; }); \ > __kcsan_enable_current(); \ > __v; \ > }); \ > }) > > had me confused, but then you've got this squirreled away in another > header: > > #ifdef __SANITIZE_THREAD__ > /* > * Only calls into the runtime when the particular compilation unit has KCSAN > * instrumentation enabled. May be used in header files. > */ > #define kcsan_check_access __kcsan_check_access > > /* > * Only use these to disable KCSAN for accesses in the current compilation > unit; > * calls into libraries may still perform KCSAN checks. > */ > #define __kcsan_disable_current kcsan_disable_current > #define __kcsan_enable_current kcsan_enable_current_nowarn > #else > static inline void kcsan_check_access(const volatile void *ptr, size_t size, > int type) { } > static inline void __kcsan_enable_current(void) { } > static inline void __kcsan_disable_current(void) { } > #endif > > And I suppose KCSAN_SANITIZE := n, results in __SANITIZE_THREAD__ not > being defined. > > I really hate the function attribute situation, that is some ill > considered trainwreck. > > Looking at this more, I found you already have: > > arch/x86/kernel/Makefile:KCSAN_SANITIZE := n > arch/x86/kernel/Makefile:KCOV_INSTRUMENT := n > arch/x86/mm/Makefile:KCSAN_SANITIZE := n > > So how about I complete that and kill everhthing for all arch/x86/ that > has DEFINE_IDTENTRY*() in. > > That avoids me having to do a lot of work to split up the tricky bits. > You didn't think it was important, so why should I bother. > > So then I end up with something like the below, and I've validated that > does not generate instrumentation... HOWEVER, I now need ~10g of memory > and many seconds to compile each file in arch/x86/kernel/. > > That is, when I do 'make arch/x86/kernel/ -j8', it is slow enough that I > can run top and grab: > > 31249 root 20 0 6128580 4.1g 13092 R 100.0 13.1 0:16.29 cc1 > 31278 root 20 0 6259456 4.4g 12932 R 100.0 13.9 0:16.27 cc1 > 31286 root 20 0 7243160 4.9g 13028 R 100.0 15.5 0:16.26 cc1 > 31289 root 20 0 5933824 4.0g 12936 R 100.0 12.8 0:16.26 cc1 > 31331 root 20 0 4250924 2.9g 13016 R 100.0 9.3 0:09.54 cc1 > 31346 root 20 0 1939552 1.3g 13028 R 100.0 4.1 0:07.01 cc1 > 31238 root 20 0 6293524 4.1g 13008 R 100.0 13.0 0:16.29 cc1 > 31259 root 20 0 6817076 4.7g 12956 R 100.0 14.9 0:16.27 cc1 > > and it then triggers OOMs, while previously I could build kernels with > -j80 on that machine: > > 31289 root 20 0 10.8g 6.2g 884 R 100.0 19.7 1:01.56 cc1 > 31249 root 20 0 10.2g 6.1g 484 R 100.0 19.3 1:00.10 cc1 > 31331 root 20 0 10.3g 7.2g 496 R 100.0 23.1 0:53.95 cc1 > > Only 3 left, because the others OOM'ed. > > This is gcc-8.3, the situation with gcc-10 seems marginally better, but > still atrocious. > > --- > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > index b7a5790d8d63..ff959f0209e7 100644 > --- a/arch/x86/entry/Makefile > +++ b/arch/x86/entry/Makefile > @@ -6,6 +6,7 @@ > KASAN_SANITIZE := n > UBSAN_SANITIZE := n > KCOV_INSTRUMENT := n > +KCSAN_INSTRUMENT := n > > CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector > -fstack-protector-strong > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector > -fstack-protector-strong > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index d6d61c4455fa..f2a46a87026e 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -22,15 +22,18 @@ CFLAGS_REMOVE_early_printk.o = -pg > CFLAGS_REMOVE_head64.o = -pg > endif > > -KASAN_SANITIZE_head$(BITS).o := n > -KASAN_SANITIZE_dumpstack.o := n > -KASAN_SANITIZE_dumpstack_$(BITS).o := n > -KASAN_SANITIZE_stacktrace.o := n > -KASAN_SANITIZE_paravirt.o := n > - > -# With some compiler versions the generated code results in boot hangs, > caused > -# by several compilation units. To be safe, disable all instrumentation. > -KCSAN_SANITIZE := n > +# > +# You cannot instrument entry code, that results in definite problems. > +# In particular, anything with DEFINE_IDTENTRY*() in must not have > +# instrumentation on. > +# > +# If only function attributes and inlining would work properly, without > +# that untangling this is a giant trainwreck, don't attempt. > +# > +KASAN_SANITIZE := n > +UBSAN_SANITIZE := n > +KCOV_INSTRUMENT := n > +KCSAN_INSTRUMENT := n > > OBJECT_FILES_NON_STANDARD_test_nx.o := y > OBJECT_FILES_NON_STANDARD_paravirt_patch.o := y > @@ -39,11 +42,6 @@ ifdef CONFIG_FRAME_POINTER > OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y > endif > > -# If instrumentation of this dir is enabled, boot hangs during first second. > -# Probably could be more selective here, but note that files related to irqs, > -# boot, dumpstack/stacktrace, etc are either non-interesting or can lead to > -# non-deterministic coverage. > -KCOV_INSTRUMENT := n > > CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace > > diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile > index f7fd0e868c9c..f8d7e7432847 100644 > --- a/arch/x86/mm/Makefile > +++ b/arch/x86/mm/Makefile > @@ -1,15 +1,17 @@ > # SPDX-License-Identifier: GPL-2.0 > -# Kernel does not boot with instrumentation of tlb.c and mem_encrypt*.c > -KCOV_INSTRUMENT_tlb.o := n > -KCOV_INSTRUMENT_mem_encrypt.o := n > -KCOV_INSTRUMENT_mem_encrypt_identity.o := n > > -KASAN_SANITIZE_mem_encrypt.o := n > -KASAN_SANITIZE_mem_encrypt_identity.o := n > - > -# Disable KCSAN entirely, because otherwise we get warnings that some > functions > -# reference __initdata sections. > -KCSAN_SANITIZE := n > +# > +# You cannot instrument entry code, that results in definite problems. > +# In particular, anything with DEFINE_IDTENTRY*() in must not have > +# instrumentation on. > +# > +# If only function attributes and inlining would work properly, without > +# that untangling this is a giant trainwreck, don't attempt. > +# > +KASAN_SANITIZE := n > +UBSAN_SANITIZE := n > +KCOV_INSTRUMENT := n > +KCSAN_INSTRUMENT := n > > ifdef CONFIG_FUNCTION_TRACER > CFLAGS_REMOVE_mem_encrypt.o = -pg > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 3bb962959d8b..48f85d1d2db6 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -241,7 +241,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, > int val, > * atomicity or dependency ordering guarantees. Note that this may result > * in tears! > */ > -#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x)) > +#define __READ_ONCE(x) data_race((*(const volatile __unqual_scalar_typeof(x) > *)&(x))) > > #define __READ_ONCE_SCALAR(x) \ > ({ \ > @@ -260,7 +260,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, > int val, > > #define __WRITE_ONCE(x, val) \ > do { \ > - *(volatile typeof(x) *)&(x) = (val); \ > + data_race(*(volatile typeof(x) *)&(x) = (val)); \ > } while (0) > > #define __WRITE_ONCE_SCALAR(x, val) \ >
Disabling most instrumentation for arch/x86 is reasonable. Also fine with the __READ_ONCE/__WRITE_ONCE changes (your improved compiler-friendlier version). We likely can't have both: still instrument __READ_ONCE/__WRITE_ONCE (as Will suggested) *and* avoid double-instrumentation in arch_atomic. If most use-cases of __READ_ONCE/__WRITE_ONCE are likely to use data_race() or KCSAN_SANITIZE := n anyway, I'd say it's reasonable for now. Thanks, -- Marco
