xfs: define bug_on_assert debug mode sysfs tunable

In DEBUG mode, assert failures unconditionally trigger a kernel BUG.
This is useful in diagnostic situations to panic a system and
collect detailed state information at the time of a failure.

This can also cause problems in cases where DEBUG mode code is
desired but it is preferable not trigger kernel BUGs on assert
failure. For example, during development of new code or during
certain xfstests tests that intentionally cause corruption and test
the kernel for survival (but otherwise may expect to trigger assert
failures).

To provide additional flexibility, create the
<sysfs>/fs/xfs/debug/bug_on_assert tunable to configure assert
failure behavior at runtime. This tunable is only available in DEBUG
mode and is enabled by default to preserve existing default
behavior. When disabled, assert failures in DEBUG mode result in
kernel warnings.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_globals.c

@@ -47,4 +47,6 @@ xfs_param_t xfs_params = {
 
 struct xfs_globals xfs_globals = {
 	.log_recovery_delay	=	0,	/* no delay by default */
+	.bug_on_assert		=	true,	/* historical default in DEBUG
+						 * mode */
 };

fs/xfs/xfs_message.c

@@ -110,7 +110,10 @@ assfail(char *expr, char *file, int line)
 {
 	xfs_emerg(NULL, "Assertion failed: %s, file: %s, line: %d",
 		expr, file, line);
-	BUG();
+	if (xfs_globals.bug_on_assert)
+		BUG();
+	else
+		WARN_ON(1);
 }
 
 void

fs/xfs/xfs_sysctl.h

@@ -95,6 +95,7 @@ extern xfs_param_t	xfs_params;
 
 struct xfs_globals {
 	int	log_recovery_delay;	/* log recovery delay (secs) */
+	bool	bug_on_assert;		/* BUG() the kernel on assert failure */
 };
 extern struct xfs_globals	xfs_globals;
 

fs/xfs/xfs_sysfs.c

@@ -145,6 +145,38 @@ struct kobj_type xfs_mp_ktype = {
 #ifdef DEBUG
 /* debug */
 
+STATIC ssize_t
+bug_on_assert_store(
+	struct kobject		*kobject,
+	const char		*buf,
+	size_t			count)
+{
+	int			ret;
+	int			val;
+
+	ret = kstrtoint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	if (val == 1)
+		xfs_globals.bug_on_assert = true;
+	else if (val == 0)
+		xfs_globals.bug_on_assert = false;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+STATIC ssize_t
+bug_on_assert_show(
+	struct kobject		*kobject,
+	char			*buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.bug_on_assert ? 1 : 0);
+}
+XFS_SYSFS_ATTR_RW(bug_on_assert);
+
 STATIC ssize_t
 log_recovery_delay_store(
 	struct kobject	*kobject,
@@ -176,6 +208,7 @@ log_recovery_delay_show(
 XFS_SYSFS_ATTR_RW(log_recovery_delay);
 
 static struct attribute *xfs_dbg_attrs[] = {
+	ATTR_LIST(bug_on_assert),
 	ATTR_LIST(log_recovery_delay),
 	NULL,
 };