/* SPDX-License-Identifier: GPL-2.0 *//* * Special rules for ignoring entire classes of data-racy memory accesses. None * of the rules here imply that such data races are generally safe! * * All rules in this file can be configured via CONFIG_KCSAN_PERMISSIVE. Keep * them separate from core code to make it easier to audit. * * Copyright (C) 2019, Google LLC. */ #ifndef _KERNEL_KCSAN_PERMISSIVE_H#define _KERNEL_KCSAN_PERMISSIVE_H #include <linux/bitops.h>#include <linux/sched.h>#include <linux/types.h> /* * Access ignore rules based on address. */static __always_inline bool kcsan_ignore_address(const volatile void *ptr){	if (!IS_ENABLED(CONFIG_KCSAN_PERMISSIVE))		return false; 	/*	 * Data-racy bitops on current->flags are too common, ignore completely	 * for now.	 */	return ptr == &current->flags;} /* * Data race ignore rules based on access type and value change patterns. */static boolkcsan_ignore_data_race(size_t size, int type, u64 old, u64 new, u64 diff){	if (!IS_ENABLED(CONFIG_KCSAN_PERMISSIVE))		return false; 	/*	 * Rules here are only for plain read accesses, so that we still report	 * data races between plain read-write accesses.	 */	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;} #endif /* _KERNEL_KCSAN_PERMISSIVE_H */