Kernel Concurrency Sanitizer (KCSAN) updates for v6.13

- Fixes to make KCSAN compatible with PREEMPT_RT
 
 - Minor cleanups
 
 All changes have been in linux-next for the past 4 weeks.
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Merge tag 'kcsan-20241112-v6.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/melver/linux

Pull Kernel Concurrency Sanitizer (KCSAN) updates from Marco Elver:

 - Make KCSAN compatible with PREEMPT_RT

 - Minor cleanup

* tag 'kcsan-20241112-v6.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/melver/linux:
  kcsan: Remove redundant call of kallsyms_lookup_name()
  kcsan: Turn report_filterlist_lock into a raw_spinlock

kernel/kcsan/debugfs.c

@@ -46,14 +46,8 @@ static struct {
 	int		used;		/* number of elements used */
 	bool		sorted;		/* if elements are sorted */
 	bool		whitelist;	/* if list is a blacklist or whitelist */
-} report_filterlist = {
-	.addrs		= NULL,
-	.size		= 8,		/* small initial size */
-	.used		= 0,
-	.sorted		= false,
-	.whitelist	= false,	/* default is blacklist */
-};
-static DEFINE_SPINLOCK(report_filterlist_lock);
+} report_filterlist;
+static DEFINE_RAW_SPINLOCK(report_filterlist_lock);
 
 /*
  * The microbenchmark allows benchmarking KCSAN core runtime only. To run
@@ -110,7 +104,7 @@ bool kcsan_skip_report_debugfs(unsigned long func_addr)
 		return false;
 	func_addr -= offset; /* Get function start */
 
-	spin_lock_irqsave(&report_filterlist_lock, flags);
+	raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 	if (report_filterlist.used == 0)
 		goto out;
 
@@ -127,7 +121,7 @@ bool kcsan_skip_report_debugfs(unsigned long func_addr)
 		ret = !ret;
 
 out:
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 	return ret;
 }
 
@@ -135,9 +129,9 @@ static void set_report_filterlist_whitelist(bool whitelist)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&report_filterlist_lock, flags);
+	raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 	report_filterlist.whitelist = whitelist;
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 }
 
 /* Returns 0 on success, error-code otherwise. */
@@ -145,6 +139,9 @@ static ssize_t insert_report_filterlist(const char *func)
 {
 	unsigned long flags;
 	unsigned long addr = kallsyms_lookup_name(func);
+	unsigned long *delay_free = NULL;
+	unsigned long *new_addrs = NULL;
+	size_t new_size = 0;
 	ssize_t ret = 0;
 
 	if (!addr) {
@@ -152,42 +149,42 @@ static ssize_t insert_report_filterlist(const char *func)
 		return -ENOENT;
 	}
 
-	spin_lock_irqsave(&report_filterlist_lock, flags);
+retry_alloc:
+	/*
+	 * Check if we need an allocation, and re-validate under the lock. Since
+	 * the report_filterlist_lock is a raw, cannot allocate under the lock.
+	 */
+	if (data_race(report_filterlist.used == report_filterlist.size)) {
+		new_size = (report_filterlist.size ?: 4) * 2;
+		delay_free = new_addrs = kmalloc_array(new_size, sizeof(unsigned long), GFP_KERNEL);
+		if (!new_addrs)
+			return -ENOMEM;
+	}
 
-	if (report_filterlist.addrs == NULL) {
-		/* initial allocation */
-		report_filterlist.addrs =
-			kmalloc_array(report_filterlist.size,
-				      sizeof(unsigned long), GFP_ATOMIC);
-		if (report_filterlist.addrs == NULL) {
-			ret = -ENOMEM;
-			goto out;
-		}
-	} else if (report_filterlist.used == report_filterlist.size) {
-		/* resize filterlist */
-		size_t new_size = report_filterlist.size * 2;
-		unsigned long *new_addrs =
-			krealloc(report_filterlist.addrs,
-				 new_size * sizeof(unsigned long), GFP_ATOMIC);
-
-		if (new_addrs == NULL) {
-			/* leave filterlist itself untouched */
-			ret = -ENOMEM;
-			goto out;
+	raw_spin_lock_irqsave(&report_filterlist_lock, flags);
+	if (report_filterlist.used == report_filterlist.size) {
+		/* Check we pre-allocated enough, and retry if not. */
+		if (report_filterlist.used >= new_size) {
+			raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
+			kfree(new_addrs); /* kfree(NULL) is safe */
+			delay_free = new_addrs = NULL;
+			goto retry_alloc;
 		}
 
+		if (report_filterlist.used)
+			memcpy(new_addrs, report_filterlist.addrs, report_filterlist.used * sizeof(unsigned long));
+		delay_free = report_filterlist.addrs; /* free the old list */
+		report_filterlist.addrs = new_addrs;  /* switch to the new list */
 		report_filterlist.size = new_size;
-		report_filterlist.addrs = new_addrs;
 	}
 
 	/* Note: deduplicating should be done in userspace. */
-	report_filterlist.addrs[report_filterlist.used++] =
-		kallsyms_lookup_name(func);
+	report_filterlist.addrs[report_filterlist.used++] = addr;
 	report_filterlist.sorted = false;
 
-out:
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 
+	kfree(delay_free);
 	return ret;
 }
 
@@ -204,13 +201,13 @@ static int show_info(struct seq_file *file, void *v)
 	}
 
 	/* show filter functions, and filter type */
-	spin_lock_irqsave(&report_filterlist_lock, flags);
+	raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 	seq_printf(file, "\n%s functions: %s\n",
 		   report_filterlist.whitelist ? "whitelisted" : "blacklisted",
 		   report_filterlist.used == 0 ? "none" : "");
 	for (i = 0; i < report_filterlist.used; ++i)
 		seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 
 	return 0;
 }