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>
>
> I think it seems reasonable, though I really wish that other patchset to
> clean up all the "modify thread state when we start/end transactions"
> had landed.
>
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> --D
>
> > ---
> > 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
> > @@ -261,6 +261,7 @@ xfs_trans_alloc(
> > {
> > struct xfs_trans *tp;
> > int error;
> > + bool retried = false;
> >
> > /*
> > * Allocate the handle before we do our freeze accounting and setting up
> > @@ -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.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
