Fix a problem that occurs when the filesystem fills up.

When the filesystem is able to allocate an indirect block but not the data
block, it incorrectly unwinds the indirect block leaving a dangling pointer
to a free block.
This is said to fix the "freeing free block" panics people were seeing.

From FreeBSD.

diff --git a/sys/ufs/ffs/ffs_balloc.c b/sys/ufs/ffs/ffs_balloc.c
index a3cea28..76f91db 100644 (file)
--- a/sys/ufs/ffs/ffs_balloc.c
+++ b/sys/ufs/ffs/ffs_balloc.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: ffs_balloc.c,v 1.9 1999/05/27 20:36:21 art Exp $      */
+/*     $OpenBSD: ffs_balloc.c,v 1.10 2000/04/20 14:41:57 art Exp $     */
 /*     $NetBSD: ffs_balloc.c,v 1.3 1996/02/09 22:22:21 christos Exp $  */
 
 /*
@@ -88,6 +88,7 @@ ffs_balloc(v)
        daddr_t newb, *bap, pref;
        int deallocated, osize, nsize, num, i, error;
        daddr_t *allocib, *blkp, *allocblk, allociblk[NIADDR+1];
+       int unwindidx = -1;
 
        vp = ap->a_vp;
        ip = VTOI(vp);
@@ -292,6 +293,8 @@ ffs_balloc(v)
                         }
                }
                bap[indirs[i - 1].in_off] = nb;
+               if (allocib == NULL && unwindidx < 0)
+                       unwindidx = i - 1;
                /*
                 * If required, write synchronously, otherwise use
                 * delayed write.
@@ -358,8 +361,23 @@ fail:
                ffs_blkfree(ip, *blkp, fs->fs_bsize);
                deallocated += fs->fs_bsize;
        }
-       if (allocib != NULL)
+       if (allocib != NULL) {
                *allocib = 0;
+       } else if (unwindidx >= 0) {
+               int r;
+
+               r = bread(vp, indirs[unwindidx].in_lbn, 
+                   (int)fs->fs_bsize, NOCRED, &bp);
+               if (r)
+                       panic("Could not unwind indirect block, error %d", r);
+               bap = (ufs_daddr_t *)bp->b_data;
+               bap[indirs[unwindidx].in_off] = 0;
+               if (flags & B_SYNC) {
+                       bwrite(bp);
+               } else {
+                       bdwrite(bp);
+               }
+       }
        if (deallocated) {
 #ifdef QUOTA
                /*
@@ -370,6 +388,6 @@ fail:
                ip->i_ffs_blocks -= btodb(deallocated);
                ip->i_flag |= IN_CHANGE | IN_UPDATE;
        }
-       return (error);
 
+       return (error);
 }