diff options
Diffstat (limited to 'kernel/kcsan/permissive.h')
| -rw-r--r-- | kernel/kcsan/permissive.h | 49 |
1 files changed, 48 insertions, 1 deletions
diff --git a/kernel/kcsan/permissive.h b/kernel/kcsan/permissive.h index f90e30800c11..2c01fe4a59ee 100644 --- a/kernel/kcsan/permissive.h +++ b/kernel/kcsan/permissive.h @@ -12,6 +12,8 @@ #ifndef _KERNEL_KCSAN_PERMISSIVE_H #define _KERNEL_KCSAN_PERMISSIVE_H +#include <linux/bitops.h> +#include <linux/sched.h> #include <linux/types.h> /* @@ -22,7 +24,11 @@ static __always_inline bool kcsan_ignore_address(const volatile void *ptr) if (!IS_ENABLED(CONFIG_KCSAN_PERMISSIVE)) return false; - return false; + /* + * Data-racy bitops on current->flags are too common, ignore completely + * for now. + */ + return ptr == ¤t->flags; } /* @@ -41,6 +47,47 @@ kcsan_ignore_data_race(size_t size, int type, u64 old, u64 new, u64 diff) if (type || size > sizeof(long)) return false; + /* + * A common pattern is checking/setting just 1 bit in a variable; for + * example: + * + * if (flags & SOME_FLAG) { ... } + * + * and elsewhere flags is updated concurrently: + * + * flags |= SOME_OTHER_FLAG; // just 1 bit + * + * While it is still recommended that such accesses be marked + * appropriately, in many cases these types of data races are so common + * that marking them all is often unrealistic and left to maintainer + * preference. + * + * The assumption in all cases is that with all known compiler + * optimizations (including those that tear accesses), because no more + * than 1 bit changed, the plain accesses are safe despite the presence + * of data races. + * + * The rules here will ignore the data races if we observe no more than + * 1 bit changed. + * + * Of course many operations can effecively change just 1 bit, but the + * general assuption that data races involving 1-bit changes can be + * tolerated still applies. + * + * And in case a true bug is missed, the bug likely manifests as a + * reportable data race elsewhere. + */ + if (hweight64(diff) == 1) { + /* + * Exception: Report data races where the values look like + * ordinary booleans (one of them was 0 and the 0th bit was + * changed) More often than not, they come with interesting + * memory ordering requirements, so let's report them. + */ + if (!((!old || !new) && diff == 1)) + return true; + } + return false; } |