From: Jan Kara Subject: Re: [PATCH] ext4: fix off-by-one on max nr_pages in ext4_find_unwritten_pgoff() Date: Tue, 23 May 2017 10:34:32 +0200 Message-ID: <20170523083432.GE1230@quack2.suse.cz> References: <20170521080026.20986-1-eguan@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org To: Eryu Guan Return-path: Received: from mx2.suse.de ([195.135.220.15]:40520 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1759734AbdEWIee (ORCPT ); Tue, 23 May 2017 04:34:34 -0400 Content-Disposition: inline In-Reply-To: <20170521080026.20986-1-eguan@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sun 21-05-17 16:00:26, Eryu Guan wrote: > ext4_find_unwritten_pgoff() is used to search for offset of hole or > data in page range [index, end] (both inclusive), and the max number > of pages to search should be at least one, if end == index. > Otherwise the only page is missed and no hole or data is found, > which is not correct. > > When block size is smaller than page size, this can be demonstrated > by preallocating a file with size smaller than page size and writing > data to the last block. E.g. run this xfs_io command on a 1k block > size ext4 on x86_64 host. > > # xfs_io -fc "falloc 0 3k" -c "pwrite 2k 1k" \ > -c "seek -d 0" /mnt/ext4/testfile > wrote 1024/1024 bytes at offset 2048 > 1 KiB, 1 ops; 0.0000 sec (42.459 MiB/sec and 43478.2609 ops/sec) > Whence Result > DATA EOF > > Data at offset 2k was missed, and lseek(2) returned ENXIO. > > This is unconvered by generic/285 subtest 07 and 08 on ppc64 host, > where pagesize is 64k. Because a recent change to generic/285 > reduced the preallocated file size to smaller than 64k. > > Cc: stable@vger.kernel.org # v3.7+ > Signed-off-by: Eryu Guan Yeah, thanks for fixing this! Actually this is a bug introduced by my recent fixes. Previously, 'end' used to be "one block after the end" and so the math worked out correctly :-|. You can add: Reviewed-by: Jan Kara Honza > --- > fs/ext4/file.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index 831fd6b..7b206e5 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -481,7 +481,7 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, > int i, num; > unsigned long nr_pages; > > - num = min_t(pgoff_t, end - index, PAGEVEC_SIZE); > + num = min_t(pgoff_t, end - index, PAGEVEC_SIZE - 1) + 1; > nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index, > (pgoff_t)num); > if (nr_pages == 0) { > -- > 2.9.4 > -- Jan Kara SUSE Labs, CR