Messages in this thread Patch in this message | | | Date | Thu, 21 May 2020 16:20:39 +0200 | Subject | [PATCH -tip v3 03/11] kcsan: Support distinguishing volatile accesses | From | Marco Elver <> |
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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().
Acked-by: Will Deacon <will@kernel.org> Signed-off-by: Marco Elver <elver@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); + /* * The below are not required by KCSAN, but can still be emitted by the * compiler. diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan index 20337a7ecf54..75d2942b9437 100644 --- a/scripts/Makefile.kcsan +++ b/scripts/Makefile.kcsan @@ -9,7 +9,10 @@ else cc-param = --param -$(1) endif +# Keep most options here optional, to allow enabling more compilers if absence +# of some options does not break KCSAN nor causes false positive reports. CFLAGS_KCSAN := -fsanitize=thread \ - $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) + $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \ + $(call cc-param,tsan-distinguish-volatile=1) endif # CONFIG_KCSAN -- 2.26.2.761.g0e0b3e54be-goog
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