Re: Assertions tripping in xfs/104

Darrick J. Wong
2019-04-16T18:59:47Z

On Tue, Apr 16, 2019 at 02:23:46PM -0400, Brian Foster wrote:
> On Tue, Apr 16, 2019 at 08:26:39AM -0700, Darrick J. Wong wrote:
> > On Tue, Apr 16, 2019 at 08:00:59AM -0400, Brian Foster wrote:
> > > On Mon, Apr 15, 2019 at 06:53:28PM -0700, Darrick J. Wong wrote:
> > > > Hi Brian,
> > > >
> > > > When running fstests against what will become the xfs-5.2-merge tree, I
> > > > hit an assert in xfs/104; the dmesg for that is pasted below.
> > > >
> > > > I'm pretty sure that what's going on here is that we hit a deferred AGFL
> > > > free while growing the filesystem and need to do a defer_roll, but
> > > > tr_growdata is not one of the permanent reservation transactions and
> > > > that's why we trip some asserts.
> > > >
> > >
> > > Yeah, it looks like we can hit this in the case where a growfs extends
> > > the last pre-existing AG in the fs. We "free" the additional space into
> > > the AG, happen to come across an overpopulated AGFL and end up doing
> > > deferred ops from a non-permanent transaction.
> > >
> > > I think we should probably just update the tr_growdata transaction to
> > > reflect how it's used and mark it permanent with the default permanent
> > > log count (2). That obviously increases the reservation size, but it's
> > > not like grow is a high frequency or performance critical operation.
> > >
> > > > FSTYP -- xfs (debug)
> > > > PLATFORM -- Linux/x86_64 mtr01 5.1.0-rc5-djw
> > > > MKFS_OPTIONS -- -f -m reflink=1,rmapbt=1, -i sparse=1, -b size=1024, /dev/sdd
> > > > MOUNT_OPTIONS -- -o usrquota,grpquota,prjquota, /dev/sdd /opt
> > > >
> > > > Granted this is the first time I've seen this in several months of
> > > > nightly fstests runs, so chances are this one is hard to reproduce.
> > > >
> > >
> > > I don't recall seeing this and don't reproduce in a few iterations of
> > > xfs/104 with the above geometry. I'll keep trying for a bit. In the
> > > meantime, a diff is appended if you'd like to give that a try. Thoughts?
> >
> > That looks reasonable, though I think we end up playing whackamole
> > trying to find all the transactions that could result in a deferred agfl
> > free on a non-permanent transaction type.
> >
> > Maybe a debugging patch along the lines of:
> >
> > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> > index 857a53e58b94..e597164641a1 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.c
> > +++ b/fs/xfs/libxfs/xfs_alloc.c
> > @@ -2324,6 +2324,8 @@ xfs_alloc_fix_freelist(
> > targs.oinfo = XFS_RMAP_OINFO_SKIP_UPDATE;
> > else
> > targs.oinfo = XFS_RMAP_OINFO_AG;
> > + ASSERT((flags & XFS_ALLOC_FLAG_NOSHRINK) ||
> > + (tp->t_flags & XFS_TRANS_PERM_LOG_RES));
> > while (!(flags & XFS_ALLOC_FLAG_NOSHRINK) && pag->pagf_flcount > need) {
> > error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
> > if (error)
> >
> > Though this is a blunt instrument since as we've seen with x/104 not all
> > of the freelist fix calls ever result in shrinking the agfl.
> >
>
> Yeah, but I think it's a reasonable rule given the current
> implementation of unconditionally deferring AGFL frees. This certainly
> would have helped detect this situation when this functionality was
> initially added. I'll send a patch with the transaction fixup and this
> assert once I get it through some testing.

Ok. I started a test run with just the assert to see if I could weed
out any more problem transactions and I'll let you know if it finds any.

--D

> Brian
>
>
> > --D
> >
> > > Brian
> > >
> > > --- 8< ---
> > >
> > > diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
> > > index f99a7aefe418..83f4ee2afc49 100644
> > > --- a/fs/xfs/libxfs/xfs_trans_resv.c
> > > +++ b/fs/xfs/libxfs/xfs_trans_resv.c
> > > @@ -876,9 +876,13 @@ xfs_trans_resv_calc(
> > > resp->tr_sb.tr_logres = xfs_calc_sb_reservation(mp);
> > > resp->tr_sb.tr_logcount = XFS_DEFAULT_LOG_COUNT;
> > >
> > > + /* growdata requires permanent res; it can free space to the last AG */
> > > + resp->tr_growdata.tr_logres = xfs_calc_growdata_reservation(mp);
> > > + resp->tr_growdata.tr_logcount = XFS_DEFAULT_PERM_LOG_COUNT;
> > > + resp->tr_growdata.tr_logflags |= XFS_TRANS_PERM_LOG_RES;
> > > +
> > > /* The following transaction are logged in logical format */
> > > resp->tr_ichange.tr_logres = xfs_calc_ichange_reservation(mp);
> > > - resp->tr_growdata.tr_logres = xfs_calc_growdata_reservation(mp);
> > > resp->tr_fsyncts.tr_logres = xfs_calc_swrite_reservation(mp);
> > > resp->tr_writeid.tr_logres = xfs_calc_writeid_reservation(mp);
> > > resp->tr_attrsetrt.tr_logres = xfs_calc_attrsetrt_reservation(mp);