[Linux-cachefs] [PATCH v12 3/4] xfs: refactor the usage around xfs_trans_context_{set, clear}

[Yafang Shao]

On Thu, Dec 10, 2020 at 3:52 AM Darrick J. Wong <darrick.wong at oracle.com> wrote:
>
> On Wed, Dec 09, 2020 at 09:11:45PM +0800, Yafang Shao wrote:
> > The xfs_trans context should be active after it is allocated, and
> > deactive when it is freed.
> >
> > So these two helpers are refactored as,
> > - xfs_trans_context_set()
> >   Used in xfs_trans_alloc()
> > - xfs_trans_context_clear()
> >   Used in xfs_trans_free()
> >
> > This patch is based on Darrick's work to fix the issue in xfs/141 in the
> > earlier version. [1]
> >
> > 1. https://lore.kernel.org/linux-xfs/20201104001649.GN7123@magnolia
> >
> > Cc: Darrick J. Wong <darrick.wong at oracle.com>
> > Cc: Matthew Wilcox (Oracle) <willy at infradead.org>
> > Cc: Christoph Hellwig <hch at lst.de>
> > Cc: Dave Chinner <david at fromorbit.com>
> > Signed-off-by: Yafang Shao <laoar.shao at gmail.com>
> > ---
> >  fs/xfs/xfs_trans.c | 28 +++++++++++++++-------------
> >  1 file changed, 15 insertions(+), 13 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > index 11d390f0d3f2..4f4645329bb2 100644
> > --- a/fs/xfs/xfs_trans.c
> > +++ b/fs/xfs/xfs_trans.c
> > @@ -67,6 +67,17 @@ xfs_trans_free(
> >       xfs_extent_busy_sort(&tp->t_busy);
> >       xfs_extent_busy_clear(tp->t_mountp, &tp->t_busy, false);
> >
> > +
> > +     /* Detach the transaction from this thread. */
> > +     ASSERT(current->journal_info != NULL);
> > +     /*
> > +      * The PF_MEMALLOC_NOFS is bound to the transaction itself instead
> > +      * of the reservation, so we need to check if tp is still the
> > +      * current transaction before clearing the flag.
> > +      */
> > +     if (current->journal_info == tp)
>
> Um, you don't start setting journal_info until the next patch, so this
> means that someone who lands on this commit with git bisect will have a
> xfs with broken logic.
>
> Because this is the patch that changes where we set and restore NOFS
> context, I think you have to introduce xfs_trans_context_swap here,
> and not in the next patch.
>

Thanks for the review. I will change it in the next version.

> I also think the _swap routine has to move the old NOFS state to the
> new transaction's t_pflags,

Sure

> and then set NOFS in the old transaction's
> t_pflags so that when we clear the context on the old transaction we
> don't actually change the thread's NOFS state.
>

Both thread's NOFS state and thead's journal_info state can't be
changed in that case, right ?
So should it better be,

    __xfs_trans_commit(tp, regrant)
        xfs_trans_free(tp, regrant)
            if (!regrant). // don't clear the xfs_trans_context if
regrant is true.
                xfs_trans_context_clear()



> --D
>
> > +             xfs_trans_context_clear(tp);
> > +
> >       trace_xfs_trans_free(tp, _RET_IP_);
> >       if (!(tp->t_flags & XFS_TRANS_NO_WRITECOUNT))
> >               sb_end_intwrite(tp->t_mountp->m_super);
> > @@ -153,9 +164,6 @@ xfs_trans_reserve(
> >       int                     error = 0;
> >       bool                    rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
> >
> > -     /* Mark this thread as being in a transaction */
> > -     xfs_trans_context_set(tp);
> > -
> >       /*
> >        * Attempt to reserve the needed disk blocks by decrementing
> >        * the number needed from the number available.  This will
> > @@ -163,10 +171,9 @@ xfs_trans_reserve(
> >        */
> >       if (blocks > 0) {
> >               error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
> > -             if (error != 0) {
> > -                     xfs_trans_context_clear(tp);
> > +             if (error != 0)
> >                       return -ENOSPC;
> > -             }
> > +
> >               tp->t_blk_res += blocks;
> >       }
> >
> > @@ -241,8 +248,6 @@ xfs_trans_reserve(
> >               tp->t_blk_res = 0;
> >       }
> >
> > -     xfs_trans_context_clear(tp);
> > -
> >       return error;
> >  }
> >
> > @@ -284,6 +289,8 @@ xfs_trans_alloc(
> >       INIT_LIST_HEAD(&tp->t_dfops);
> >       tp->t_firstblock = NULLFSBLOCK;
> >
> > +     /* Mark this thread as being in a transaction */
> > +     xfs_trans_context_set(tp);
> >       error = xfs_trans_reserve(tp, resp, blocks, rtextents);
> >       if (error) {
> >               xfs_trans_cancel(tp);
> > @@ -878,7 +885,6 @@ __xfs_trans_commit(
> >
> >       xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
> >
> > -     xfs_trans_context_clear(tp);
> >       xfs_trans_free(tp);
> >
> >       /*
> > @@ -911,7 +917,6 @@ __xfs_trans_commit(
> >               tp->t_ticket = NULL;
> >       }
> >
> > -     xfs_trans_context_clear(tp);
> >       xfs_trans_free_items(tp, !!error);
> >       xfs_trans_free(tp);
> >
> > @@ -971,9 +976,6 @@ xfs_trans_cancel(
> >               tp->t_ticket = NULL;
> >       }
> >
> > -     /* mark this thread as no longer being in a transaction */
> > -     xfs_trans_context_clear(tp);
> > -
> >       xfs_trans_free_items(tp, dirty);
> >       xfs_trans_free(tp);
> >  }
> > --
> > 2.18.4
> >



-- 
Thanks
Yafang