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-rw-r--r--kernel/kcsan/permissive.h49
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 == &current->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;
}