xfs: Introduce XFS_PTAG_VERIFIER_ERROR panic mask

Currently we have a few PTAGs in place allowing us to transform a filesystem
error in a BUG() call. However, we don't have a panic tag for corrupt
metadata, so introduce XFS_PTAG_VERIFIER_ERROR so that the administrator can
use the fs.xfs.panic_mask sysctl knob to convert any error detected by buffer
verifiers into a kernel panic.

Signed-off-by: Marco Benatto <[e-mail]>
Reviewed-by: Eric Sandeen <[e-mail]>
[darrick: light editing of commit message]
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Darrick J. Wong <[e-mail]>

Documentation/filesystems/xfs.txt

···
 		XFS_ERRLEVEL_LOW:       1
 		XFS_ERRLEVEL_HIGH:      5
 
-  fs.xfs.panic_mask		(Min: 0  Default: 0  Max: 255)
+  fs.xfs.panic_mask		(Min: 0  Default: 0  Max: 256)
 	Causes certain error conditions to call BUG(). Value is a bitmask;
 	OR together the tags which represent errors which should cause panics:
 
···
 		XFS_PTAG_SHUTDOWN_IOERROR       0x00000020
 		XFS_PTAG_SHUTDOWN_LOGERROR      0x00000040
 		XFS_PTAG_FSBLOCK_ZERO           0x00000080
+		XFS_PTAG_VERIFIER_ERROR         0x00000100
 
 	This option is intended for debugging only.
 

fs/xfs/xfs_error.c

···
 	fa = failaddr ? failaddr : __return_address;
 	__xfs_buf_ioerror(bp, error, fa);
 
-	xfs_alert(mp, "Metadata %s detected at %pS, %s block 0x%llx %s",
+	xfs_alert_tag(mp, XFS_PTAG_VERIFIER_ERROR,
+		  "Metadata %s detected at %pS, %s block 0x%llx %s",
 		  bp->b_error == -EFSBADCRC ? "CRC error" : "corruption",
 		  fa, bp->b_ops->name, bp->b_bn, name);
 

fs/xfs/xfs_error.h

···
 #define		XFS_PTAG_SHUTDOWN_IOERROR	0x00000020
 #define		XFS_PTAG_SHUTDOWN_LOGERROR	0x00000040
 #define		XFS_PTAG_FSBLOCK_ZERO		0x00000080
+#define		XFS_PTAG_VERIFIER_ERROR		0x00000100
 
 #endif	/* __XFS_ERROR_H__ */

fs/xfs/xfs_globals.c

···
 			  /*	MIN		DFLT		MAX	*/
 	.sgid_inherit	= {	0,		0,		1	},
 	.symlink_mode	= {	0,		0,		1	},
-	.panic_mask	= {	0,		0,		255	},
+	.panic_mask	= {	0,		0,		256	},
 	.error_level	= {	0,		3,		11	},
 	.syncd_timer	= {	1*100,		30*100,		7200*100},
 	.stats_clear	= {	0,		0,		1	},