From: Eric Whitney Subject: Re: [PATCH] e2fsck: fix multiply-claimed block quota accounting when deleting files Date: Thu, 11 May 2017 11:42:35 -0400 Message-ID: <20170511154235.GA11505@localhost.localdomain> References: <20170510220440.GA26875@localhost.localdomain> <6A0785D3-A3D1-45F7-AD67-3C52D7364551@dilger.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Whitney , linux-ext4@vger.kernel.org, tytso@mit.edu To: Andreas Dilger Return-path: Received: from mail-qk0-f194.google.com ([209.85.220.194]:33884 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754545AbdEKPkb (ORCPT ); Thu, 11 May 2017 11:40:31 -0400 Received: by mail-qk0-f194.google.com with SMTP id u75so4171783qka.1 for ; Thu, 11 May 2017 08:40:31 -0700 (PDT) Content-Disposition: inline In-Reply-To: <6A0785D3-A3D1-45F7-AD67-3C52D7364551@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org List-ID: * Andreas Dilger : > > > On May 10, 2017, at 4:04 PM, Eric Whitney wrote: > > > > As e2fsck processes each file in pass1, the actual file system quota is > > increased by the number of blocks discovered in the file. This can > > include both non-multiply-claimed and multiply-claimed blocks, if the > > latter exist. However, if a file containing multiply-claimed blocks > > is then deleted in pass1b, those blocks are not taken into account when > > decreasing the actual quota. In this case, the new quota values written > > to the file system by e2fsck overstate the space actually consumed. > > And, e2fsck must be run twice on the file system to fully correct > > quota. > > > > Fix this by counting multiply-claimed blocks as a debit to quota when > > deleting files in pass1b. > > Nice catch. It would be good to have an e2fsck test case that checks this. > Also, one minor code style nit (or possibly defect) below. Yeah, there's not much test coverage in this area. I'll look at it. > > > Signed-off-by: Eric Whitney > > --- > > e2fsck/pass1b.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/e2fsck/pass1b.c b/e2fsck/pass1b.c > > index b40f026..8744fad 100644 > > --- a/e2fsck/pass1b.c > > +++ b/e2fsck/pass1b.c > > @@ -636,11 +636,13 @@ static int delete_file_block(ext2_filsys fs, > > lc = EXT2FS_B2C(fs, blockcnt); > > if (ext2fs_test_block_bitmap2(ctx->block_dup_map, *block_nr)) { > > n = dict_lookup(&clstr_dict, INT_TO_VOIDPTR(c)); > > - if (n) { > > - p = (struct dup_cluster *) dnode_get(n); > > - if (lc != pb->cur_cluster) > > decrement_badcount(ctx, *block_nr, p); > > - } else > > + if (n) > > + if (lc != pb->cur_cluster) { > > + p = (struct dup_cluster *) dnode_get(n); > > decrement_badcount(ctx, *block_nr, p); > > + pb->dup_blocks++; > > + } > > + else > > com_err("delete_file_block", 0, > > _("internal error: can't find dup_blk for %llu\n"), > > *block_nr); > > This is tricky to know which "if" the "else" is for without the added braces, > and to be honest I don't even know what the C standard says about this, which > is likely why the braces were there in the first place. I would instead > recommend to add braces around the "else" clause to make it clear. > Yes, that's a classic dangling else bug - I scrubbed too hard. Thanks very much for finding that. V2 coming along shortly. Thanks for the review, Eric