From: =?UTF-8?Q?Andreas_Gr=C3=BCnbacher?= Subject: Re: [PATCH] ext4: Fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize Date: Fri, 28 Jul 2017 13:40:25 +0200 Message-ID: References: <20170728111637.12473-1-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Ted Tso , linux-ext4@vger.kernel.org, Andreas Gruenbacher , stable@vger.kernel.org To: Jan Kara Return-path: Received: from mail-yw0-f194.google.com ([209.85.161.194]:36794 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751071AbdG1Lk1 (ORCPT ); Fri, 28 Jul 2017 07:40:27 -0400 In-Reply-To: <20170728111637.12473-1-jack@suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: 2017-07-28 13:16 GMT+02:00 Jan Kara : > ext4_find_unwritten_pgoff() does not properly handle a situation when > starting index is in the middle of a page and blocksize < pagesize. The > following command shows the bug on filesystem with 1k blocksize: > > xfs_io -f -c "falloc 0 4k" \ > -c "pwrite 1k 1k" \ > -c "pwrite 3k 1k" \ > -c "seek -a -r 0" foo > > In this example, neither lseek(fd, 1024, SEEK_HOLE) nor lseek(fd, 2048, > SEEK_DATA) will return the correct result. > > Fix the problem by neglecting buffers in a page before starting offset. This looks correct as a minimal fix for 4.13. We can later switch to page_cache_seek_hole_data which does the same thing as ext4_find_unwritten_pgoff, or directly to iomap_seek_{hole,data}. > Reported-by: Andreas Gruenbacher > CC: stable@vger.kernel.org > Signed-off-by: Jan Kara > --- > fs/ext4/file.c | 3 +++ > 1 file changed, 3 insertions(+) > > This is an easy fix for the SEEK_HOLE/SEEK_DATA bug Andreas found. Longer > term we want to move ext4 to use page_cache_seek_hole_data() however for > stable backporting this is more suitable. > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index b221d0b546b0..8ba34cbe8fe7 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -530,6 +530,8 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, > lastoff = page_offset(page); > bh = head = page_buffers(page); > do { > + if (lastoff + bh->b_size <= startoff) > + goto next; > if (buffer_uptodate(bh) || > buffer_unwritten(bh)) { > if (whence == SEEK_DATA) > @@ -544,6 +546,7 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, > unlock_page(page); > goto out; > } > +next: > lastoff += bh->b_size; > bh = bh->b_this_page; > } while (bh != head); > -- > 2.12.3 Thanks, Andreas