xfs: define fatal assert build time tunable

While configurable at runtime, the DEBUG mode assert failure
behavior is usually either desired or not for a particular
situation. For example, developers using kernel modules may prefer
for fatal asserts to remain disabled across module reloads while QE
engineers doing broad regression testing may prefer to have fatal
asserts enabled on boot to facilitate data collection for bug
reports.

To provide a compromise/convenience for developers, create a Kconfig
option that sets the default value of the DEBUG mode 'bug_on_assert'
sysfs tunable. The default behavior remains to trigger kernel BUGs
on assert failures to preserve existing behavior across kernel
configuration updates with DEBUG mode enabled.

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/Kconfig

@@ -96,3 +96,16 @@ config XFS_DEBUG
 	  not useful unless you are debugging a particular problem.
 
 	  Say N unless you are an XFS developer, or you play one on TV.
+
+config XFS_ASSERT_FATAL
+	bool "XFS fatal asserts"
+	default y
+	depends on XFS_FS && XFS_DEBUG
+	help
+	  Set the default DEBUG mode ASSERT failure behavior.
+
+	  Say Y here to cause DEBUG mode ASSERT failures to result in fatal
+	  errors that BUG() the kernel by default. If you say N, ASSERT failures
+	  result in warnings.
+
+	  This behavior can be modified at runtime via sysfs.

fs/xfs/xfs.h

@@ -24,6 +24,10 @@
 #define XFS_BUF_LOCK_TRACKING 1
 #endif
 
+#ifdef CONFIG_XFS_ASSERT_FATAL
+#define XFS_ASSERT_FATAL 1
+#endif
+
 #ifdef CONFIG_XFS_WARN
 #define XFS_WARN 1
 #endif

fs/xfs/xfs_globals.c

@@ -47,6 +47,9 @@ 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 */
+#ifdef XFS_ASSERT_FATAL
+	.bug_on_assert		=	true,	/* assert failures BUG() */
+#else
+	.bug_on_assert		=	false,	/* assert failures WARN() */
+#endif
 };