From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Monakhov Subject: Re: [PATCH 08/10] ext4: endless truncate due to nonlocked dio readers V2 Date: Thu, 27 Sep 2012 19:11:13 +0400 Message-ID: <87626z5wmm.fsf@openvz.org> References: <1348487060-19598-1-git-send-email-dmonakhov@openvz.org> <1348487060-19598-9-git-send-email-dmonakhov@openvz.org> <20120926140538.GH10145@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz, lczerner@redhat.com To: Jan Kara Return-path: Received: from mail-la0-f46.google.com ([209.85.215.46]:34008 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752533Ab2I0PLR (ORCPT ); Thu, 27 Sep 2012 11:11:17 -0400 Received: by lagh6 with SMTP id h6so460044lag.19 for ; Thu, 27 Sep 2012 08:11:16 -0700 (PDT) In-Reply-To: <20120926140538.GH10145@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 26 Sep 2012 16:05:38 +0200, Jan Kara wrote: > On Mon 24-09-12 15:44:18, Dmitry Monakhov wrote: > > If we have enough aggressive DIO readers, truncate and other dio > > waiters will wait forever inside inode_dio_wait(). It is reasonable > > to disable nonlock DIO read optimization during truncate. > Umm, actually this is a problem with any inode_dio_wait() call in ext4, > isn't it? So I'd just create ext4_inode_dio_wait() doing > ext4_inode_block_unlocked_dio(inode); > inode_dio_wait(inode); > ext4_inode_resume_unlocked_dio(inode); > > and use it instead of inode_dio_wait(). Ops sorry miss that comment. Actually all other places are very special, and guarded already: 1) ext4_ext_punch_hole() 2) ext4_move_extents() 3) ext4_change_inode_journal_flag() Such functions require explicit scope where nonlocked DIO read should be disabled. So ext4_setattr() is the only place where we wait for existing dio, but nonlocked dio reads are allowed and may result in temporal live-lock. > > Honza > > > Signed-off-by: Dmitry Monakhov > > --- > > fs/ext4/inode.c | 8 ++++++-- > > 1 files changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index 32e9701..d3f86e7 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -4330,9 +4330,13 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr) > > if (attr->ia_valid & ATTR_SIZE) { > > if (attr->ia_size != inode->i_size) { > > truncate_setsize(inode, attr->ia_size); > > - /* Inode size will be reduced, wait for dio in flight */ > > - if (orphan) > > + /* Inode size will be reduced, wait for dio in flight. > > + * Temproraly disable unlocked DIO to prevent livelock */ > ^^ Temporarily > > > + if (orphan) { > > + ext4_inode_block_unlocked_dio(inode); > > inode_dio_wait(inode); > > + ext4_inode_resume_unlocked_dio(inode); > > + } > > } > > ext4_truncate(inode); > > } > > -- > > 1.7.7.6 > > > -- > Jan Kara > SUSE Labs, CR > -- > 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