Patchwork [44/74] e2fsck: only release clusters when shortening a directory during a rehash

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Submitter Darrick J. Wong
Date Dec. 11, 2013, 1:23 a.m.
Message ID <20131211012312.30655.85205.stgit@birch.djwong.org>
Download mbox | patch
Permalink /patch/299713/
State Superseded
Headers show

Comments

Darrick J. Wong - Dec. 11, 2013, 1:23 a.m.
When the rehash process is running on a bigalloc filesystem, it
compresses all the directory entries and hash structures into the
beginning of the directory file and then uses block_iterate3() to free
the blocks off the end of the file.  It seems to call
ext2fs_block_alloc_stats2() for every block in a cluster, which is
unfortunate because this function allocates and frees entire clusters
(and updates the summary counts accordingly).  In this case e2fsck
writes out incorrect summary counts.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 e2fsck/rehash.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)



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Theodore Ts'o - Dec. 16, 2013, 4:55 a.m.
On Tue, Dec 10, 2013 at 05:23:12PM -0800, Darrick J. Wong wrote:
> When the rehash process is running on a bigalloc filesystem, it
> compresses all the directory entries and hash structures into the
> beginning of the directory file and then uses block_iterate3() to free
> the blocks off the end of the file.  It seems to call
> ext2fs_block_alloc_stats2() for every block in a cluster, which is
> unfortunate because this function allocates and frees entire clusters
> (and updates the summary counts accordingly).  In this case e2fsck
> writes out incorrect summary counts.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Thanks, applied.

					- Ted
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Patch

diff --git a/e2fsck/rehash.c b/e2fsck/rehash.c
index 20704a9..9b90353 100644
--- a/e2fsck/rehash.c
+++ b/e2fsck/rehash.c
@@ -719,10 +719,18 @@  static int write_dir_block(ext2_filsys fs,
 		/* We don't need this block, so release it */
 		e2fsck_read_bitmaps(wd->ctx);
 		blk = *block_nr;
-		ext2fs_unmark_block_bitmap2(wd->ctx->block_found_map, blk);
-		ext2fs_block_alloc_stats2(fs, blk, -1);
+		/*
+		 * In theory, we only release blocks from the end of the
+		 * directory file, so it's fine to clobber a whole cluster at
+		 * once.
+		 */
+		if (blk % EXT2FS_CLUSTER_RATIO(fs) == 0) {
+			ext2fs_unmark_block_bitmap2(wd->ctx->block_found_map,
+						    blk);
+			ext2fs_block_alloc_stats2(fs, blk, -1);
+			wd->cleared++;
+		}
 		*block_nr = 0;
-		wd->cleared++;
 		return BLOCK_CHANGED;
 	}