Re: [PATCH 4/8] kcsan: Add missing CONFIG_KCSAN_IGNORE_ATOMICS checks
From: Marco Elver
Date: Tue Jul 21 2020 - 10:21:44 EST
On Tue, 21 Jul 2020 at 16:09, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jul 21, 2020 at 12:30:12PM +0200, Marco Elver wrote:
> > Add missing CONFIG_KCSAN_IGNORE_ATOMICS checks for the builtin atomics
> > instrumentation.
> >
> > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > ---
> > Added to this series, as it would otherwise cause patch conflicts.
> > ---
> > kernel/kcsan/core.c | 25 +++++++++++++++++--------
> > 1 file changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index 4633baebf84e..f53524ea0292 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -892,14 +892,17 @@ EXPORT_SYMBOL(__tsan_init);
> > u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder); \
> > u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder) \
> > { \
> > - check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC); \
> > + if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) \
> > + check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC); \
> > return __atomic_load_n(ptr, memorder); \
> > } \
> > EXPORT_SYMBOL(__tsan_atomic##bits##_load); \
> > void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder); \
> > void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder) \
> > { \
> > - check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > + if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) \
> > + check_access(ptr, bits / BITS_PER_BYTE, \
> > + KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > __atomic_store_n(ptr, v, memorder); \
> > } \
> > EXPORT_SYMBOL(__tsan_atomic##bits##_store)
> > @@ -908,8 +911,10 @@ EXPORT_SYMBOL(__tsan_init);
> > u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder); \
> > u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder) \
> > { \
> > - check_access(ptr, bits / BITS_PER_BYTE, \
> > - KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > + if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) \
> > + check_access(ptr, bits / BITS_PER_BYTE, \
> > + KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
> > + KCSAN_ACCESS_ATOMIC); \
> > return __atomic_##op##suffix(ptr, v, memorder); \
> > } \
> > EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
> > @@ -937,8 +942,10 @@ EXPORT_SYMBOL(__tsan_init);
> > int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \
> > u##bits val, int mo, int fail_mo) \
> > { \
> > - check_access(ptr, bits / BITS_PER_BYTE, \
> > - KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > + if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) \
> > + check_access(ptr, bits / BITS_PER_BYTE, \
> > + KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
> > + KCSAN_ACCESS_ATOMIC); \
> > return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo); \
> > } \
> > EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
> > @@ -949,8 +956,10 @@ EXPORT_SYMBOL(__tsan_init);
> > u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
> > int mo, int fail_mo) \
> > { \
> > - check_access(ptr, bits / BITS_PER_BYTE, \
> > - KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
> > + if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) \
> > + check_access(ptr, bits / BITS_PER_BYTE, \
> > + KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
> > + KCSAN_ACCESS_ATOMIC); \
> > __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo); \
> > return exp; \
> > } \
>
>
> *groan*, that could really do with a bucket of '{', '}'. Also, it is
> inconsistent in style with the existing use in
> DEFINE_TSAN_VOLATILE_READ_WRITE() where the define causes an early
> return.
Sadly we can't do an early return because we must always execute what
comes after the check. Unlike normal read/write instrumentation, TSAN
instrumentation for builtin atomics replaces the atomic with a call
into the runtime, and the runtime must also execute the atomic.
I'll add the {}.
Thanks,
-- Marco