On Fri, Feb 19, 2021 at 03:56:58PM +1100, Dave Chinner wrote:
> On Thu, Feb 18, 2021 at 07:23:09PM -0800, Darrick J. Wong wrote:
> > On Thu, Feb 18, 2021 at 03:14:58PM -0500, Brian Foster wrote:
> > > fstest xfs/167 produced a lockdep splat that complained about a
> > > nested transaction acquiring freeze protection during an eofblocks
> > > scan. Drop freeze protection around the block reclaim scan in the
> > > transaction allocation code to avoid this problem.
> > >
> > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
...
> > > fs/xfs/xfs_trans.c | 19 ++++++++++++++-----
> > > 1 file changed, 14 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > > index 44f72c09c203..c32c62d3b77a 100644
> > > --- a/fs/xfs/xfs_trans.c
> > > +++ b/fs/xfs/xfs_trans.c
...
> > > @@ -288,19 +289,27 @@ xfs_trans_alloc(
> > > INIT_LIST_HEAD(&tp->t_dfops);
> > > tp->t_firstblock = NULLFSBLOCK;
> > >
> > > +retry:
> > > error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > - if (error == -ENOSPC) {
> > > + if (error == -ENOSPC && !retried) {
> > > /*
> > > * We weren't able to reserve enough space for the transaction.
> > > * Flush the other speculative space allocations to free space.
> > > * Do not perform a synchronous scan because callers can hold
> > > * other locks.
> > > */
> > > + retried = true;
> > > + if (!(flags & XFS_TRANS_NO_WRITECOUNT))
> > > + sb_end_intwrite(mp->m_super);
> > > error = xfs_blockgc_free_space(mp, NULL);
> > > - if (!error)
> > > - error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> > > - }
> > > - if (error) {
> > > + if (error) {
> > > + kmem_cache_free(xfs_trans_zone, tp);
> > > + return error;
> > > + }
>
> This seems dangerous to me. If xfs_trans_reserve() adds anything to
> the transaction even if it fails, this will fail to free it. e.g.
> xfs_log_reserve() call allocate a ticket and attach it to the
> transaction and *then fail*. This code will now leak that ticket.
>
xfs_trans_reserve() ungrants the log ticket (which frees it, at least in
the allocation case) and disassociates from the transaction on error, so
I don't see how this causes any problems.
Brian
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
>
