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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        kernel-team@fb.com, mingo@kernel.org
Cc:     elver@google.com, andreyknvl@google.com, glider@google.com,
        dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com,
        Mark Rutland <mark.rutland@arm.com>,
        "Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 08/10] kcsan: Remove kcsan_report_type
Date:   Tue, 11 May 2021 16:23:59 -0700
Message-Id: <20210511232401.2896217-8-paulmck@kernel.org>
In-Reply-To: <20210511231149.GA2895263@paulmck-ThinkPad-P17-Gen-1>
References: <20210511231149.GA2895263@paulmck-ThinkPad-P17-Gen-1>
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From: Mark Rutland <mark.rutland@arm.com>

Now that the reporting code has been refactored, it's clear by
construction that print_report() can only be passed
KCSAN_REPORT_RACE_SIGNAL or KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, and these
can also be distinguished by the presence of `other_info`.

Let's simplify things and remove the report type enum, and instead let's
check `other_info` to distinguish these cases. This allows us to remove
code for cases which are impossible and generally makes the code simpler.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[ elver@google.com: add updated comments to kcsan_report_*() functions ]
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/kcsan/kcsan.h  | 33 +++++++++++++--------------------
 kernel/kcsan/report.c | 29 +++++++----------------------
 2 files changed, 20 insertions(+), 42 deletions(-)

diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 2ee43fd5d6a4..572f119a19eb 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -116,32 +116,25 @@ enum kcsan_value_change {
 	KCSAN_VALUE_CHANGE_TRUE,
 };
 
-enum kcsan_report_type {
-	/*
-	 * The thread that set up the watchpoint and briefly stalled was
-	 * signalled that another thread triggered the watchpoint.
-	 */
-	KCSAN_REPORT_RACE_SIGNAL,
-
-	/*
-	 * A thread found and consumed a matching watchpoint.
-	 */
-	KCSAN_REPORT_CONSUMED_WATCHPOINT,
-
-	/*
-	 * No other thread was observed to race with the access, but the data
-	 * value before and after the stall differs.
-	 */
-	KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
-};
-
 /*
- * Notify the report code that a race occurred.
+ * The calling thread hit and consumed a watchpoint: set the access information
+ * to be consumed by the reporting thread. No report is printed yet.
  */
 void kcsan_report_set_info(const volatile void *ptr, size_t size, int access_type,
 			   int watchpoint_idx);
+
+/*
+ * The calling thread observed that the watchpoint it set up was hit and
+ * consumed: print the full report based on information set by the racing
+ * thread.
+ */
 void kcsan_report_known_origin(const volatile void *ptr, size_t size, int access_type,
 			       enum kcsan_value_change value_change, int watchpoint_idx);
+
+/*
+ * No other thread was observed to race with the access, but the data value
+ * before and after the stall differs. Reports a race of "unknown origin".
+ */
 void kcsan_report_unknown_origin(const volatile void *ptr, size_t size, int access_type);
 
 #endif /* _KERNEL_KCSAN_KCSAN_H */
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index ba924f110c95..50cee2357885 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -326,7 +326,6 @@ static void print_verbose_info(struct task_struct *task)
 }
 
 static void print_report(enum kcsan_value_change value_change,
-			 enum kcsan_report_type type,
 			 const struct access_info *ai,
 			 const struct other_info *other_info)
 {
@@ -343,7 +342,7 @@ static void print_report(enum kcsan_value_change value_change,
 	if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
 		return;
 
-	if (type == KCSAN_REPORT_RACE_SIGNAL) {
+	if (other_info) {
 		other_skipnr = get_stack_skipnr(other_info->stack_entries,
 						other_info->num_stack_entries);
 		other_frame = other_info->stack_entries[other_skipnr];
@@ -358,8 +357,7 @@ static void print_report(enum kcsan_value_change value_change,
 
 	/* Print report header. */
 	pr_err("==================================================================\n");
-	switch (type) {
-	case KCSAN_REPORT_RACE_SIGNAL: {
+	if (other_info) {
 		int cmp;
 
 		/*
@@ -371,22 +369,15 @@ static void print_report(enum kcsan_value_change value_change,
 		       get_bug_type(ai->access_type | other_info->ai.access_type),
 		       (void *)(cmp < 0 ? other_frame : this_frame),
 		       (void *)(cmp < 0 ? this_frame : other_frame));
-	} break;
-
-	case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:
+	} else {
 		pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(ai->access_type),
 		       (void *)this_frame);
-		break;
-
-	default:
-		BUG();
 	}
 
 	pr_err("\n");
 
 	/* Print information about the racing accesses. */
-	switch (type) {
-	case KCSAN_REPORT_RACE_SIGNAL:
+	if (other_info) {
 		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
 		       get_access_type(other_info->ai.access_type), other_info->ai.ptr,
 		       other_info->ai.size, get_thread_desc(other_info->ai.task_pid),
@@ -404,16 +395,10 @@ static void print_report(enum kcsan_value_change value_change,
 		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
 		       get_access_type(ai->access_type), ai->ptr, ai->size,
 		       get_thread_desc(ai->task_pid), ai->cpu_id);
-		break;
-
-	case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:
+	} else {
 		pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",
 		       get_access_type(ai->access_type), ai->ptr, ai->size,
 		       get_thread_desc(ai->task_pid), ai->cpu_id);
-		break;
-
-	default:
-		BUG();
 	}
 	/* Print stack trace of this thread. */
 	stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
@@ -623,7 +608,7 @@ void kcsan_report_known_origin(const volatile void *ptr, size_t size, int access
 	 * be done once we know the full stack trace in print_report().
 	 */
 	if (value_change != KCSAN_VALUE_CHANGE_FALSE)
-		print_report(value_change, KCSAN_REPORT_RACE_SIGNAL, &ai, other_info);
+		print_report(value_change, &ai, other_info);
 
 	release_report(&flags, other_info);
 out:
@@ -640,7 +625,7 @@ void kcsan_report_unknown_origin(const volatile void *ptr, size_t size, int acce
 	lockdep_off(); /* See kcsan_report_known_origin(). */
 
 	raw_spin_lock_irqsave(&report_lock, flags);
-	print_report(KCSAN_VALUE_CHANGE_TRUE, KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, &ai, NULL);
+	print_report(KCSAN_VALUE_CHANGE_TRUE, &ai, NULL);
 	raw_spin_unlock_irqrestore(&report_lock, flags);
 
 	lockdep_on();
-- 
2.31.1.189.g2e36527f23