From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:50138 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726801AbeGaN1g (ORCPT ); Tue, 31 Jul 2018 09:27:36 -0400 Date: Tue, 31 Jul 2018 07:47:36 -0400 From: Brian Foster Subject: Re: [PATCH 01/15] xfs: refactor internal dfops initialization Message-ID: <20180731114735.GA40201@bfoster> References: <20180730164520.36882-1-bfoster@redhat.com> <20180730164520.36882-2-bfoster@redhat.com> <20180730193048.GB30972@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180730193048.GB30972@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org On Mon, Jul 30, 2018 at 12:30:48PM -0700, Darrick J. Wong wrote: > On Mon, Jul 30, 2018 at 12:45:06PM -0400, Brian Foster wrote: > > The current transaction allocation code conditionally initializes > > the ->t_dfops indirection pointer. Transaction commit/cancel check > > the validity of the pointer to determine whether to finish/cancel > > the internal dfops. > > > > This disallows the ability to use the internal dfops list as a > > temporary container (via xfs_trans_alloc_empty()). Refactor > > transaction allocation to always initialize ->t_dfops and check > > permanent reservation state on transaction commit/cancel. > > > > Signed-off-by: Brian Foster > > --- > > fs/xfs/xfs_trans.c | 12 +++--------- > > 1 file changed, 3 insertions(+), 9 deletions(-) > > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > index 7bf5c1202719..8d3b7f28b193 100644 > > --- a/fs/xfs/xfs_trans.c > > +++ b/fs/xfs/xfs_trans.c > > @@ -281,13 +281,7 @@ xfs_trans_alloc( > > INIT_LIST_HEAD(&tp->t_items); > > INIT_LIST_HEAD(&tp->t_busy); > > tp->t_firstblock = NULLFSBLOCK; > > - /* > > - * We only roll transactions with permanent log reservation. Don't init > > - * ->t_dfops to skip attempts to finish or cancel an empty dfops with a > > - * non-permanent res. > > - */ > > - if (resp->tr_logflags & XFS_TRANS_PERM_LOG_RES) > > - xfs_defer_init(tp, &tp->t_dfops_internal); > > + xfs_defer_init(tp, &tp->t_dfops_internal); > > > > error = xfs_trans_reserve(tp, resp, blocks, rtextents); > > if (error) { > > @@ -932,7 +926,7 @@ __xfs_trans_commit( > > trace_xfs_trans_commit(tp, _RET_IP_); > > > > /* finish deferred items on final commit */ > > - if (!regrant && tp->t_dfops) { > > + if (!regrant && (tp->t_flags & XFS_TRANS_PERM_LOG_RES)) { > > The usage model of deferred ops is that one has to create a transaction > with a permanent reservation, and only then start attaching deferred ops > to the dfops inside the transaction. It's a programming error if a > caller tries to finish deferred ops using a non-permanent transaction, > and prior to this patch t_dfops would be NULL and we'd blow up > immediately in xfs_defer_add(..., tp->t_dfops, ...); > > However, now that we initialize t_dfops unconditionally, won't this > cause the above programming mistake to leak silently any incorrectly > queued defer ops? > Yeah, I'm not sure the previous behavior was really appropriate in that regard either. I'll add the xfs_defer_add() assert suggested by Christoph. We could also add a WARN_ON_ONCE() or something in the commit path to make sure we never see a !perm transaction with dfops, if you think that's useful..? Brian > --D > > > error = xfs_defer_finish_noroll(&tp); > > if (error) { > > xfs_defer_cancel(tp); > > @@ -1029,7 +1023,7 @@ xfs_trans_cancel( > > > > trace_xfs_trans_cancel(tp, _RET_IP_); > > > > - if (tp->t_dfops) > > + if (tp->t_flags & XFS_TRANS_PERM_LOG_RES) > > xfs_defer_cancel(tp); > > > > /* > > -- > > 2.17.1 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html