From: Dmitri Monakhov Subject: Re: [PATCH] ext4: Fix discard of inode prealloc space with delayed allocation. Date: Wed, 25 Feb 2009 19:57:52 +0300 Message-ID: References: <1235578922-7790-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: tytso@mit.edu, linux-ext4@vger.kernel.org To: "Aneesh Kumar K.V" Return-path: Received: from mailhub.sw.ru ([195.214.232.25]:34405 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754736AbZBYQ7h (ORCPT ); Wed, 25 Feb 2009 11:59:37 -0500 In-Reply-To: <1235578922-7790-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> (Aneesh Kumar K. V.'s message of "Wed\, 25 Feb 2009 21\:52\:02 +0530") Sender: linux-ext4-owner@vger.kernel.org List-ID: "Aneesh Kumar K.V" writes: > With delayed allocation we should not/cannot discard inode prealloc space > during file close. We would still have dirty pages for which we haven't allocated > blocks yet. With this fix after each get_blocks request we check whether we have > zero reserved blocks and if yes and we don't have any writers on the file we > discard inode prealloc space. > > Signed-off-by: Aneesh Kumar K.V > > --- > fs/ext4/file.c | 9 ++++++++- > fs/ext4/inode.c | 6 ++++++ > 2 files changed, 14 insertions(+), 1 deletions(-) > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index f731cb5..4e468e2 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -33,9 +33,16 @@ > */ > static int ext4_release_file(struct inode *inode, struct file *filp) > { > + int rsv_data_blocks; > + > + spin_lock(&EXT4_I(inode)->i_block_reservation_lock); > + rsv_data_blocks = EXT4_I(inode)->i_reserved_data_blocks; > + spin_unlock(&EXT4_I(inode)->i_block_reservation_lock); > + Seems we have race condition here because at this point someone may: 1)open file 2)then perform some write activity => (i_reserved_data_blocks != 0) 3)close file => (inode->i_writecount == 1) > /* if we are the last writer on the inode, drop the block reservation */ > if ((filp->f_mode & FMODE_WRITE) && > - (atomic_read(&inode->i_writecount) == 1)) > + (atomic_read(&inode->i_writecount) == 1) && > + !rsv_data_blocks) > { > down_write(&EXT4_I(inode)->i_data_sem); After we have grabbed i_data_sem we are protected from get_block activity, and may safely recheck i_reserved_data_blocks again here. > ext4_discard_preallocations(inode); > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 51cdd13..26dcec4 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -1038,6 +1038,12 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used) > EXT4_I(inode)->i_reserved_data_blocks -= used; > > spin_unlock(&EXT4_I(inode)->i_block_reservation_lock); > + /* > + * If have done all the pending block allocation and if the > + * we don't have any writer on the inode > + */ No problem here because we are hold i_data_sem. > + if (!total && (atomic_read(&inode->i_writecount) == 0)) > + ext4_discard_preallocations(inode); > } > > /*