xfs: introduce CONFIG_XFS_WARN

Running a CONFIG_XFS_DEBUG kernel in production environments is not
the best idea as it introduces significant overhead, can change
the behaviour of algorithms (such as allocation) to improve test
coverage, and (most importantly) panic the machine on non-fatal
errors.

There are many cases where all we want to do is run a
kernel with more bounds checking enabled, such as is provided by the
ASSERT() statements throughout the code, but without all the
potential overhead and drawbacks.

This patch converts all the ASSERT statements to evaluate as
WARN_ON(1) statements and hence if they fail dump a warning and a
stack trace to the log. This has minimal overhead and does not
change any algorithms, and will allow us to find strange "out of
bounds" problems more easily on production machines.

There are a few places where assert statements contain debug only
code. These are converted to be debug-or-warn only code so that we
still get all the assert checks in the code.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/Kconfig

@@ -69,6 +69,19 @@ config XFS_RT
 
 	  If unsure, say N.
 
+config XFS_WARN
+	bool "XFS Verbose Warnings"
+	depends on XFS_FS && !XFS_DEBUG
+	help
+	  Say Y here to get an XFS build with many additional warnings.
+	  It converts ASSERT checks to WARN, so will log any out-of-bounds
+	  conditions that occur that would otherwise be missed. It is much
+	  lighter weight than XFS_DEBUG and does not modify algorithms and will
+	  not cause the kernel to panic on non-fatal errors.
+
+	  However, similar to XFS_DEBUG, it is only advisable to use this if you
+	  are debugging a particular problem.
+
 config XFS_DEBUG
 	bool "XFS Debugging support"
 	depends on XFS_FS