On Thu, May 21, 2020 at 01:08:46PM +0200, Marco Elver wrote: > In the kernel, volatile is used in various concurrent context, whether > in low-level synchronization primitives or for legacy reasons. If > supported by the compiler, we will assume that aligned volatile accesses > up to sizeof(long long) (matching compiletime_assert_rwonce_type()) are > atomic. > > Recent versions Clang [1] (GCC tentative [2]) can instrument volatile > accesses differently. Add the option (required) to enable the > instrumentation, and provide the necessary runtime functions. None of > the updated compilers are widely available yet (Clang 11 will be the > first release to support the feature). > > [1] > https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814 > [2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html > > This patch allows removing any explicit checks in primitives such as > READ_ONCE() and WRITE_ONCE(). > > Signed-off-by: Marco Elver <el...@google.com> > --- > v2: > * Reword Makefile comment. > --- > kernel/kcsan/core.c | 43 ++++++++++++++++++++++++++++++++++++++++++ > scripts/Makefile.kcsan | 5 ++++- > 2 files changed, 47 insertions(+), 1 deletion(-) > > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c > index a73a66cf79df..15f67949d11e 100644 > --- a/kernel/kcsan/core.c > +++ b/kernel/kcsan/core.c > @@ -789,6 +789,49 @@ void __tsan_write_range(void *ptr, size_t size) > } > EXPORT_SYMBOL(__tsan_write_range); > > +/* > + * Use of explicit volatile is generally disallowed [1], however, volatile is > + * still used in various concurrent context, whether in low-level > + * synchronization primitives or for legacy reasons. > + * [1] https://lwn.net/Articles/233479/ > + * > + * We only consider volatile accesses atomic if they are aligned and would > pass > + * the size-check of compiletime_assert_rwonce_type(). > + */ > +#define DEFINE_TSAN_VOLATILE_READ_WRITE(size) > \ > + void __tsan_volatile_read##size(void *ptr) \ > + { \ > + const bool is_atomic = size <= sizeof(long long) && \ > + IS_ALIGNED((unsigned long)ptr, size); \ > + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ > + return; \ > + check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ > + } \ > + EXPORT_SYMBOL(__tsan_volatile_read##size); \ > + void __tsan_unaligned_volatile_read##size(void *ptr) \ > + __alias(__tsan_volatile_read##size); \ > + EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ > + void __tsan_volatile_write##size(void *ptr) \ > + { \ > + const bool is_atomic = size <= sizeof(long long) && \ > + IS_ALIGNED((unsigned long)ptr, size); \ > + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ > + return; \ > + check_access(ptr, size, \ > + KCSAN_ACCESS_WRITE | \ > + (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ > + } \ > + EXPORT_SYMBOL(__tsan_volatile_write##size); \ > + void __tsan_unaligned_volatile_write##size(void *ptr) \ > + __alias(__tsan_volatile_write##size); \ > + EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) > + > +DEFINE_TSAN_VOLATILE_READ_WRITE(1); > +DEFINE_TSAN_VOLATILE_READ_WRITE(2); > +DEFINE_TSAN_VOLATILE_READ_WRITE(4); > +DEFINE_TSAN_VOLATILE_READ_WRITE(8); > +DEFINE_TSAN_VOLATILE_READ_WRITE(16);
Having a 16-byte case seems a bit weird to me, but I guess clang needs this for some reason? Will
