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Date:      Wed, 28 Sep 2011 19:38:47 +0000 (UTC)
From:      Kirk McKusick <mckusick@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-other@freebsd.org
Subject:   svn commit: r225851 - stable/9/sys/ufs/ffs
Message-ID:  <201109281938.p8SJclbt087020@svn.freebsd.org>
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Author: mckusick
Date: Wed Sep 28 19:38:47 2011
New Revision: 225851
URL: http://svn.freebsd.org/changeset/base/225851

Log:
  MFC r225807:
  This update eliminates a lock-order reversal warning discovered
  whle tracking down the system hang reported in kern/160662 and
  corrected in revision 225806 (MFC'ed as 225850). The LOR is not
  the cause of the system hang and indeed cannot cause an actual
  deadlock. However, it can be easily eliminated by defering the
  acquisition of a buflock until after all the vnode locks have
  been acquired.
  
  As journaled soft updates first appeared in 9.0, this will be the
  only MFC of this change.
  
  Approved by:     re (kib)
  Reported by:     Hans Ottevanger
  PR:              kern/160662

Modified:
  stable/9/sys/ufs/ffs/ffs_snapshot.c

Modified: stable/9/sys/ufs/ffs/ffs_snapshot.c
==============================================================================
--- stable/9/sys/ufs/ffs/ffs_snapshot.c	Wed Sep 28 19:36:21 2011	(r225850)
+++ stable/9/sys/ufs/ffs/ffs_snapshot.c	Wed Sep 28 19:38:47 2011	(r225851)
@@ -212,7 +212,7 @@ ffs_snapshot(mp, snapfile)
 	struct fs *copy_fs = NULL, *fs;
 	struct thread *td = curthread;
 	struct inode *ip, *xp;
-	struct buf *bp, *nbp, *ibp, *sbp = NULL;
+	struct buf *bp, *nbp, *ibp;
 	struct nameidata nd;
 	struct mount *wrtmp;
 	struct vattr vat;
@@ -460,21 +460,14 @@ restart:
 	 * Grab a copy of the superblock and its summary information.
 	 * We delay writing it until the suspension is released below.
 	 */
-	error = bread(vp, lblkno(fs, fs->fs_sblockloc), fs->fs_bsize,
-	    KERNCRED, &sbp);
-	if (error) {
-		brelse(sbp);
-		sbp = NULL;
-		goto out1;
-	}
-	loc = blkoff(fs, fs->fs_sblockloc);
-	copy_fs = (struct fs *)(sbp->b_data + loc);
+	copy_fs = malloc((u_long)fs->fs_bsize, M_UFSMNT, M_WAITOK);
 	bcopy(fs, copy_fs, fs->fs_sbsize);
 	if ((fs->fs_flags & (FS_UNCLEAN | FS_NEEDSFSCK)) == 0)
 		copy_fs->fs_clean = 1;
 	size = fs->fs_bsize < SBLOCKSIZE ? fs->fs_bsize : SBLOCKSIZE;
 	if (fs->fs_sbsize < size)
-		bzero(&sbp->b_data[loc + fs->fs_sbsize], size - fs->fs_sbsize);
+		bzero(&((char *)copy_fs)[fs->fs_sbsize],
+		    size - fs->fs_sbsize);
 	size = blkroundup(fs, fs->fs_cssize);
 	if (fs->fs_contigsumsize > 0)
 		size += fs->fs_ncg * sizeof(int32_t);
@@ -490,8 +483,8 @@ restart:
 		    len, KERNCRED, &bp)) != 0) {
 			brelse(bp);
 			free(copy_fs->fs_csp, M_UFSMNT);
-			bawrite(sbp);
-			sbp = NULL;
+			free(copy_fs, M_UFSMNT);
+			copy_fs = NULL;
 			goto out1;
 		}
 		bcopy(bp->b_data, space, (u_int)len);
@@ -606,8 +599,8 @@ loop:
 		vdrop(xvp);
 		if (error) {
 			free(copy_fs->fs_csp, M_UFSMNT);
-			bawrite(sbp);
-			sbp = NULL;
+			free(copy_fs, M_UFSMNT);
+			copy_fs = NULL;
 			MNT_VNODE_FOREACH_ABORT(mp, mvp);
 			goto out1;
 		}
@@ -621,8 +614,8 @@ loop:
 		error = softdep_journal_lookup(mp, &xvp);
 		if (error) {
 			free(copy_fs->fs_csp, M_UFSMNT);
-			bawrite(sbp);
-			sbp = NULL;
+			free(copy_fs, M_UFSMNT);
+			copy_fs = NULL;
 			goto out1;
 		}
 		xp = VTOI(xvp);
@@ -688,8 +681,8 @@ loop:
 	VI_UNLOCK(devvp);
 	ASSERT_VOP_LOCKED(vp, "ffs_snapshot vp");
 out1:
-	KASSERT((sn != NULL && sbp != NULL && error == 0) ||
-		(sn == NULL && sbp == NULL && error != 0),
+	KASSERT((sn != NULL && copy_fs != NULL && error == 0) ||
+		(sn == NULL && copy_fs == NULL && error != 0),
 		("email phk@ and mckusick@"));
 	/*
 	 * Resume operation on filesystem.
@@ -703,7 +696,7 @@ out1:
 		    vp->v_mount->mnt_stat.f_mntonname, (long)endtime.tv_sec,
 		    endtime.tv_nsec / 1000000, redo, fs->fs_ncg);
 	}
-	if (sbp == NULL)
+	if (copy_fs == NULL)
 		goto out;
 	/*
 	 * Copy allocation information from all the snapshots in
@@ -793,6 +786,15 @@ out1:
 		space = (char *)space + fs->fs_bsize;
 		bawrite(nbp);
 	}
+	error = bread(vp, lblkno(fs, fs->fs_sblockloc), fs->fs_bsize,
+	    KERNCRED, &nbp);
+	if (error) {
+		brelse(nbp);
+	} else {
+		loc = blkoff(fs, fs->fs_sblockloc);
+		bcopy((char *)copy_fs, &nbp->b_data[loc], fs->fs_bsize);
+		bawrite(nbp);
+	}
 	/*
 	 * As this is the newest list, it is the most inclusive, so
 	 * should replace the previous list.
@@ -822,7 +824,8 @@ out1:
 		vrele(vp);		/* Drop extra reference */
 done:
 	free(copy_fs->fs_csp, M_UFSMNT);
-	bawrite(sbp);
+	free(copy_fs, M_UFSMNT);
+	copy_fs = NULL;
 out:
 	NDFREE(&nd, NDF_ONLY_PNBUF);
 	if (saved_nice > 0) {

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