svn commit: r246877 - head/sys/ufs/ffs

[Kirk McKusick]

Author: mckusick
Date: Sat Feb 16 15:11:40 2013
New Revision: 246877
URL: http://svnweb.freebsd.org/changeset/base/246877

Log:
  The UFS2 filesystem allocates new blocks of inodes as they are needed.
  When a cylinder group runs short of inodes, a new block for inodes is
  allocated, zero'ed, and written to the disk. The zero'ed inodes must
  be on the disk before the cylinder group can be updated to claim them.
  If the cylinder group claiming the new inodes were written before the
  zero'ed block of inodes, the system could crash with the filesystem in
  an unrecoverable state.
  
  Rather than adding a soft updates dependency to ensure that the new
  inode block is written before it is claimed by the cylinder group
  map, we just do a barrier write of the zero'ed inode block to ensure
  that it will get written before the updated cylinder group map can
  be written. This change should only slow down bulk loading of newly
  created filesystems since that is the primary time that new inode
  blocks need to be created.
  
  Reported by: Robert Watson
  Reviewed by: kib
  Tested by:   Peter Holm

Modified:
  head/sys/ufs/ffs/ffs_alloc.c

Modified: head/sys/ufs/ffs/ffs_alloc.c
==============================================================================
--- head/sys/ufs/ffs/ffs_alloc.c	Sat Feb 16 14:51:30 2013	(r246876)
+++ head/sys/ufs/ffs/ffs_alloc.c	Sat Feb 16 15:11:40 2013	(r246877)
@@ -1861,7 +1861,6 @@ gotit:
 	/*
 	 * Check to see if we need to initialize more inodes.
 	 */
-	ibp = NULL;
 	if (fs->fs_magic == FS_UFS2_MAGIC &&
 	    ipref + INOPB(fs) > cgp->cg_initediblk &&
 	    cgp->cg_initediblk < cgp->cg_niblk) {
@@ -1874,6 +1873,16 @@ gotit:
 			dp2->di_gen = arc4random() / 2 + 1;
 			dp2++;
 		}
+		/*
+		 * Rather than adding a soft updates dependency to ensure
+		 * that the new inode block is written before it is claimed
+		 * by the cylinder group map, we just do a barrier write
+		 * here. The barrier write will ensure that the inode block
+		 * gets written before the updated cylinder group map can be
+		 * written. The barrier write should only slow down bulk
+		 * loading of newly created filesystems.
+		 */
+		babarrierwrite(ibp);
 		cgp->cg_initediblk += INOPB(fs);
 	}
 	UFS_LOCK(ump);
@@ -1892,8 +1901,6 @@ gotit:
 	if (DOINGSOFTDEP(ITOV(ip)))
 		softdep_setup_inomapdep(bp, ip, cg * fs->fs_ipg + ipref, mode);
 	bdwrite(bp);
-	if (ibp != NULL)
-		bawrite(ibp);
 	return ((ino_t)(cg * fs->fs_ipg + ipref));
 }