[patch] kcsan: Make it RT aware

[Mike Galbraith <efault@xxxxxx>]

Converting report_filterlist_lock to raw_spinlock_t lets RT report
problem free, but makes allocations in insert_report_filterlist()
problematic.  Solve that via unlock, allocate, relock and restart.

Signed-off-by: Mike Galbraith <efault@xxxxxx>
---
 kernel/kcsan/debugfs.c |   62 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 43 insertions(+), 19 deletions(-)

--- a/kernel/kcsan/debugfs.c
+++ b/kernel/kcsan/debugfs.c
@@ -53,7 +53,7 @@ static struct {
 	.sorted		= false,
 	.whitelist	= false,	/* default is blacklist */
 };
-static DEFINE_SPINLOCK(report_filterlist_lock);
+static DEFINE_RAW_SPINLOCK(report_filterlist_lock);

 /*
  * The microbenchmark allows benchmarking KCSAN core runtime only. To run
@@ -110,7 +110,7 @@ bool kcsan_skip_report_debugfs(unsigned
 		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 +127,7 @@ bool kcsan_skip_report_debugfs(unsigned
 		ret = !ret;

 out:
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 	return ret;
 }

@@ -135,9 +135,9 @@ static void set_report_filterlist_whitel
 {
 	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. */
@@ -146,36 +146,60 @@ static ssize_t insert_report_filterlist(
 	unsigned long flags;
 	unsigned long addr = kallsyms_lookup_name(func);
 	ssize_t ret = 0;
+	int is_rt = IS_ENABLED(CONFIG_PREEMPT_RT);

 	if (!addr) {
 		pr_err("could not find function: '%s'\n", func);
 		return -ENOENT;
 	}

-	spin_lock_irqsave(&report_filterlist_lock, flags);
+	if (is_rt && !preemptible())
+		return -ENOMEM;
+
+repeat:
+	raw_spin_lock_irqsave(&report_filterlist_lock, flags);

 	if (report_filterlist.addrs == NULL) {
-		/* initial allocation */
-		report_filterlist.addrs =
-			kmalloc_array(report_filterlist.size,
+		unsigned long *array;
+		if (is_rt)
+			raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
+		array = kmalloc_array(report_filterlist.size,
 				      sizeof(unsigned long), GFP_ATOMIC);
-		if (report_filterlist.addrs == NULL) {
+		if (is_rt)
+			raw_spin_lock_irqsave(&report_filterlist_lock, flags);
+		if (!array) {
 			ret = -ENOMEM;
 			goto out;
 		}
+		if (is_rt && report_filterlist.addrs != NULL)  {
+			/* Someone beat us to it, move along to size check. */
+			raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
+			kfree(array);
+			goto repeat;
+		}
+		report_filterlist.addrs = array;
 	} 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);
-
+		size_t old_size = report_filterlist.size;
+		size_t new_size = old_size * 2;
+		unsigned long *new_addrs;
+		if (is_rt)
+			raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
+		new_addrs = krealloc(report_filterlist.addrs,
+				     new_size * sizeof(unsigned long), GFP_ATOMIC);
+		if (is_rt)
+			raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 		if (new_addrs == NULL) {
 			/* leave filterlist itself untouched */
 			ret = -ENOMEM;
 			goto out;
 		}
-
+		if (is_rt && report_filterlist.size != old_size) {
+			/* Someone else resized while we were unlocked, recheck. */
+			raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
+			kfree(new_addrs);
+			goto repeat;
+		}
 		report_filterlist.size = new_size;
 		report_filterlist.addrs = new_addrs;
 	}
@@ -186,7 +210,7 @@ static ssize_t insert_report_filterlist(
 	report_filterlist.sorted = false;

 out:
-	spin_unlock_irqrestore(&report_filterlist_lock, flags);
+	raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);

 	return ret;
 }
@@ -204,13 +228,13 @@ static int show_info(struct seq_file *fi
 	}

 	/* 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;
 }