From: =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= Subject: Re: [PATCH 07/15 v2] ext4: Take i_mutex before punching hole Date: Thu, 13 Sep 2012 11:15:03 -0400 (EDT) Message-ID: References: <1346451711-1931-1-git-send-email-lczerner@redhat.com> <1346451711-1931-8-git-send-email-lczerner@redhat.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Lukas Czerner , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, tytso@mit.edu, hughd@google.com, linux-mm@kvack.org To: Ashish Sangwan Return-path: In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, 10 Sep 2012, Ashish Sangwan wrote: > Date: Mon, 10 Sep 2012 17:30:53 +0530 > From: Ashish Sangwan > To: Lukas Czerner > Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, tytso@mit.edu, > hughd@google.com, linux-mm@kvack.org > Subject: Re: [PATCH 07/15 v2] ext4: Take i_mutex before punching hole > > On Sat, Sep 1, 2012 at 3:51 AM, Lukas Czerner wrote: > > Currently the allocation might happen in the punched range after the > > truncation and before the releasing the space of the range. This would > > lead to blocks being unallocated under the mapped buffer heads resulting > > in nasty bugs. > > > > With this commit we take i_mutex before going to do anything in the > > ext4_ext_punch_hole() preventing any write to happen while the hole > > punching is in progress. This will also allow us to ditch the writeout > > of dirty pages withing the range. > > > > This commit was based on code provided by Zheng Liu, thanks! > > > > Signed-off-by: Lukas Czerner > > --- > > fs/ext4/extents.c | 26 ++++++++++---------------- > > 1 files changed, 10 insertions(+), 16 deletions(-) > > > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > > index aabbb3f..f920383 100644 > > --- a/fs/ext4/extents.c > > +++ b/fs/ext4/extents.c > > @@ -4769,9 +4769,11 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) > > loff_t first_page_offset, last_page_offset; > > int credits, err = 0; > > > > + mutex_lock(&inode->i_mutex); > > + > > /* No need to punch hole beyond i_size */ > > if (offset >= inode->i_size) > > - return 0; > > + goto out1; > > > > /* > > * If the hole extends beyond i_size, set the hole > > @@ -4789,18 +4791,6 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) > > first_page_offset = first_page << PAGE_CACHE_SHIFT; > > last_page_offset = last_page << PAGE_CACHE_SHIFT; > > > > - /* > > - * Write out all dirty pages to avoid race conditions > > - * Then release them. > > - */ > > - if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) { > > - err = filemap_write_and_wait_range(mapping, > > - offset, offset + length - 1); > > - > > - if (err) > > - return err; > > - } > > - > > Removing above code will cause a problem in case the file has all its > data in memory and nothing has been committed on disk. If punch hole > is issued for such a file, as there are no extents present, EIO would > be returned from ext4_ext_rm_leaf. So, even though blocks would be > removed from memory, the end result will be error EIO. > > > /* Now release the pages */ > > if (last_page_offset > first_page_offset) { > > truncate_pagecache_range(inode, first_page_offset, > > To avoid this, you can add a check after the call to truncate_pagecache_range. > if(!inode->i_blocks) > return 0; Thanks for pointing this out. However Dimitry has better fix for this with some additional changes so I am dropping this particular patch. (see "ext4: punch_hole should wait for DIO writers") Thanks! -Lukas > > > @@ -4812,12 +4802,14 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) > > > > credits = ext4_writepage_trans_blocks(inode); > > handle = ext4_journal_start(inode, credits); > > - if (IS_ERR(handle)) > > - return PTR_ERR(handle); > > + if (IS_ERR(handle)) { > > + err = PTR_ERR(handle); > > + goto out1; > > + } > > > > err = ext4_orphan_add(handle, inode); > > if (err) > > - goto out; > > + goto out1; > > > > /* > > * Now we need to zero out the non-page-aligned data in the > > @@ -4907,6 +4899,8 @@ out: > > inode->i_mtime = inode->i_ctime = ext4_current_time(inode); > > ext4_mark_inode_dirty(handle, inode); > > ext4_journal_stop(handle); > > +out1: > > + mutex_unlock(&inode->i_mutex); > > return err; > > } > > int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, > > -- > > 1.7.7.6 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html >