Messages in this thread | | | Date | Tue, 27 Apr 2004 01:44:55 -0600 | From | Andreas Dilger <> | Subject | Re: [Ext2-devel] [CHECKER] warnings in fs/ext3/namei.c (2.4.19) where disk read errors get ignored, causing non-empty dir to be deleted |
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On Apr 26, 2004 23:41 -0700, Junfeng Yang wrote: > We checked EXT3 filesystem on 2.4.19 recently and found 2 cases that look > like bugs. For both of the cases, disk read errors are ignored, which > appears to cause a non-empty directory to be wrongly deleted or a dir to > contain more than one entries with identical names. > > I'm not sure if they are real bugs or not, so your confirmations > /clarifications are appericated.
I don't consider this a bug, but rather a conscious decision on the part of the developers. If you are trying to delete a directory and it has read errors, then it is better to let the unlink succeed than to refuse to unlink the directory.
> ---------------------------------------------------------------------------- > [BUG] A non-empty dir may be deleted because ext3_read errors are ignored > by ext3_find_entry. empty_dir is called whenenver ext3_rmdir tries to > remove a directory. > > > static int empty_dir (struct inode * inode) > { > bh = ext3_bread (NULL, inode, > offset >> EXT3_BLOCK_SIZE_BITS(sb), 0, &err); > if (!bh) { > #if 0 > ext3_error (sb, "empty_dir", > "directory #%lu contains a hole at offset %lu", > inode->i_ino, offset); > #endif > offset += sb->s_blocksize; > ERROR ---> continue; > } > de = (struct ext3_dir_entry_2 *) bh->b_data; > }
What is more of a bug is a few lines down. The error return from ext3_check_dir_entry() causes the rest of the directory to be skipped and "1" returned instead of skipping that block/page and continuing to check the rest of the directory. With this if there is a read error anywhere in the directory it is possible to rmdir the directory without actually deleting entries that are returned by ls.
> ---------------------------------------------------------------------------- > [BUG] A dir may end up containing more than one entries with identical > names because because disk read errors are ignored by ext3_find_entry. > ext3_find_entry is called by lots of other ext3 functions (ext3_add_entry, > ext3_unlink, ext3_rename) > > static struct buffer_head * ext3_find_entry (struct dentry *dentry, > struct ext3_dir_entry_2 ** res_dir) > { > ..... > if ((bh = bh_use[ra_ptr++]) == NULL) > goto next; > wait_on_buffer(bh); > if (!buffer_uptodate(bh)) { > /* read error, skip block & hope for the best */ > brelse(bh); > ERROR ---> goto next; > }
Again a conscious decision. If a name is potentially inaccessible because of an IO error it is better to allow the creation of a potentially duplicate name than refuse creation of any new entries in the directory. It's a matter of allowing the filesystem to be used as well as possible in the face of failures vs. just giving up and refusing to do anything.
Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
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