xfs: Add comments for usages of some macros.

Add comments explaining when to use XFS_IS_CORRUPT() and ASSERT()

Suggested-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Nirjhar-Roy-0211

fs/xfs/xfs_platform.h

@@ -235,6 +235,10 @@ int xfs_rw_bdev(struct block_device *bdev, sector_t sector, unsigned int count,
 
 #ifdef XFS_WARN
 
+/*
+ * Please note that this ASSERT doesn't kill the kernel. It will if the kernel
+ * has panic_on_warn set.
+ */
 #define ASSERT(expr)	\
 	(likely(expr) ? (void)0 : asswarn(NULL, #expr, __FILE__, __LINE__))
 
@@ -245,6 +249,11 @@ int xfs_rw_bdev(struct block_device *bdev, sector_t sector, unsigned int count,
 #endif /* XFS_WARN */
 #endif /* DEBUG */
 
+/*
+ * Use this to catch metadata corruptions that are not caught by block or
+ * structure verifiers. The reason is that the verifiers check corruptions only
+ * within the scope of the object being verified.
+ */
 #define XFS_IS_CORRUPT(mp, expr)	\
 	(unlikely(expr) ? xfs_corruption_error(#expr, XFS_ERRLEVEL_LOW, (mp), \
 					       NULL, 0, __FILE__, __LINE__, \