kcsan: Show full access type in report

This commit adds access-type information to KCSAN's reports as follows:
"read", "read (marked)", "write", and "write (marked)".

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/kcsan/core.c

@@ -255,7 +255,7 @@ static inline unsigned int get_delay(void)
 
 static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 					    size_t size,
-					    bool is_write,
+					    int type,
 					    atomic_long_t *watchpoint,
 					    long encoded_watchpoint)
 {
@@ -276,7 +276,7 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 	flags = user_access_save();
 
 	if (consumed) {
-		kcsan_report(ptr, size, is_write, true, raw_smp_processor_id(),
+		kcsan_report(ptr, size, type, true, raw_smp_processor_id(),
 			     KCSAN_REPORT_CONSUMED_WATCHPOINT);
 	} else {
 		/*
@@ -292,8 +292,9 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 }
 
 static noinline void
-kcsan_setup_watchpoint(const volatile void *ptr, size_t size, bool is_write)
+kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 {
+	const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
 	atomic_long_t *watchpoint;
 	union {
 		u8 _1;
@@ -415,13 +416,13 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, bool is_write)
 		 * No need to increment 'data_races' counter, as the racing
 		 * thread already did.
 		 */
-		kcsan_report(ptr, size, is_write, size > 8 || value_change,
+		kcsan_report(ptr, size, type, size > 8 || value_change,
 			     smp_processor_id(), KCSAN_REPORT_RACE_SIGNAL);
 	} else if (value_change) {
 		/* Inferring a race, since the value should not have changed. */
 		kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
 		if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN))
-			kcsan_report(ptr, size, is_write, true,
+			kcsan_report(ptr, size, type, true,
 				     smp_processor_id(),
 				     KCSAN_REPORT_RACE_UNKNOWN_ORIGIN);
 	}
@@ -455,10 +456,10 @@ static __always_inline void check_access(const volatile void *ptr, size_t size,
 	 */
 
 	if (unlikely(watchpoint != NULL))
-		kcsan_found_watchpoint(ptr, size, is_write, watchpoint,
+		kcsan_found_watchpoint(ptr, size, type, watchpoint,
 				       encoded_watchpoint);
 	else if (unlikely(should_watch(ptr, type)))
-		kcsan_setup_watchpoint(ptr, size, is_write);
+		kcsan_setup_watchpoint(ptr, size, type);
 }
 
 /* === Public interface ===================================================== */

kernel/kcsan/kcsan.h

@@ -103,7 +103,7 @@ enum kcsan_report_type {
 /*
  * Print a race report from thread that encountered the race.
  */
-extern void kcsan_report(const volatile void *ptr, size_t size, bool is_write,
+extern void kcsan_report(const volatile void *ptr, size_t size, int access_type,
 			 bool value_change, int cpu_id, enum kcsan_report_type type);
 
 #endif /* _KERNEL_KCSAN_KCSAN_H */

kernel/kcsan/report.c

@@ -24,7 +24,7 @@
 static struct {
 	const volatile void	*ptr;
 	size_t			size;
-	bool			is_write;
+	int			access_type;
 	int			task_pid;
 	int			cpu_id;
 	unsigned long		stack_entries[NUM_STACK_ENTRIES];
@@ -41,8 +41,10 @@ static DEFINE_SPINLOCK(report_lock);
  * Special rules to skip reporting.
  */
 static bool
-skip_report(bool is_write, bool value_change, unsigned long top_frame)
+skip_report(int access_type, bool value_change, unsigned long top_frame)
 {
+	const bool is_write = (access_type & KCSAN_ACCESS_WRITE) != 0;
+
 	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && is_write &&
 	    !value_change) {
 		/*
@@ -63,9 +65,20 @@ skip_report(bool is_write, bool value_change, unsigned long top_frame)
 	return kcsan_skip_report_debugfs(top_frame);
 }
 
-static inline const char *get_access_type(bool is_write)
+static const char *get_access_type(int type)
 {
-	return is_write ? "write" : "read";
+	switch (type) {
+	case 0:
+		return "read";
+	case KCSAN_ACCESS_ATOMIC:
+		return "read (marked)";
+	case KCSAN_ACCESS_WRITE:
+		return "write";
+	case KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
+		return "write (marked)";
+	default:
+		BUG();
+	}
 }
 
 /* Return thread description: in task or interrupt. */
@@ -112,7 +125,7 @@ static int sym_strcmp(void *addr1, void *addr2)
 /*
  * Returns true if a report was generated, false otherwise.
  */
-static bool print_report(const volatile void *ptr, size_t size, bool is_write,
+static bool print_report(const volatile void *ptr, size_t size, int access_type,
 			 bool value_change, int cpu_id,
 			 enum kcsan_report_type type)
 {
@@ -124,7 +137,7 @@ static bool print_report(const volatile void *ptr, size_t size, bool is_write,
 	/*
 	 * Must check report filter rules before starting to print.
 	 */
-	if (skip_report(is_write, true, stack_entries[skipnr]))
+	if (skip_report(access_type, true, stack_entries[skipnr]))
 		return false;
 
 	if (type == KCSAN_REPORT_RACE_SIGNAL) {
@@ -132,7 +145,7 @@ static bool print_report(const volatile void *ptr, size_t size, bool is_write,
 						other_info.num_stack_entries);
 
 		/* @value_change is only known for the other thread */
-		if (skip_report(other_info.is_write, value_change,
+		if (skip_report(other_info.access_type, value_change,
 				other_info.stack_entries[other_skipnr]))
 			return false;
 	}
@@ -170,7 +183,7 @@ static bool print_report(const volatile void *ptr, size_t size, bool is_write,
 	switch (type) {
 	case KCSAN_REPORT_RACE_SIGNAL:
 		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
-		       get_access_type(other_info.is_write), other_info.ptr,
+		       get_access_type(other_info.access_type), other_info.ptr,
 		       other_info.size, get_thread_desc(other_info.task_pid),
 		       other_info.cpu_id);
 
@@ -181,14 +194,14 @@ static bool print_report(const volatile void *ptr, size_t size, bool is_write,
 
 		pr_err("\n");
 		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
-		       get_access_type(is_write), ptr, size,
+		       get_access_type(access_type), ptr, size,
 		       get_thread_desc(in_task() ? task_pid_nr(current) : -1),
 		       cpu_id);
 		break;
 
 	case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:
 		pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",
-		       get_access_type(is_write), ptr, size,
+		       get_access_type(access_type), ptr, size,
 		       get_thread_desc(in_task() ? task_pid_nr(current) : -1),
 		       cpu_id);
 		break;
@@ -223,7 +236,7 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
  * required for the report type, simply acquires report_lock and returns true.
  */
 static bool prepare_report(unsigned long *flags, const volatile void *ptr,
-			   size_t size, bool is_write, int cpu_id,
+			   size_t size, int access_type, int cpu_id,
 			   enum kcsan_report_type type)
 {
 	if (type != KCSAN_REPORT_CONSUMED_WATCHPOINT &&
@@ -243,7 +256,7 @@ retry:
 
 		other_info.ptr			= ptr;
 		other_info.size			= size;
-		other_info.is_write		= is_write;
+		other_info.access_type		= access_type;
 		other_info.task_pid		= in_task() ? task_pid_nr(current) : -1;
 		other_info.cpu_id		= cpu_id;
 		other_info.num_stack_entries	= stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
@@ -302,14 +315,14 @@ retry:
 	goto retry;
 }
 
-void kcsan_report(const volatile void *ptr, size_t size, bool is_write,
+void kcsan_report(const volatile void *ptr, size_t size, int access_type,
 		  bool value_change, int cpu_id, enum kcsan_report_type type)
 {
 	unsigned long flags = 0;
 
 	kcsan_disable_current();
-	if (prepare_report(&flags, ptr, size, is_write, cpu_id, type)) {
-		if (print_report(ptr, size, is_write, value_change, cpu_id, type) && panic_on_warn)
+	if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) {
+		if (print_report(ptr, size, access_type, value_change, cpu_id, type) && panic_on_warn)
 			panic("panic_on_warn set ...\n");
 
 		release_report(&flags, type);