linux-kernel - Re: [PATCH] dax: Fix missed PMD wakeups

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Date:   Mon, 29 Jul 2019 08:18:52 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Boaz Harrosh <openosd@...il.com>,
        stable <stable@...r.kernel.org>,
        Robert Barror <robert.barror@...el.com>,
        Seema Pandit <seema.pandit@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dax: Fix missed PMD wakeups

On Mon, Jul 29, 2019 at 5:02 AM Jan Kara <jack@...e.cz> wrote:
>
> On Tue 16-07-19 20:39:46, Dan Williams wrote:
> > On Fri, Jul 12, 2019 at 2:14 AM Jan Kara <jack@...e.cz> wrote:
> > >
> > > On Thu 11-07-19 08:25:50, Matthew Wilcox wrote:
> > > > On Thu, Jul 11, 2019 at 07:13:50AM -0700, Matthew Wilcox wrote:
> > > > > However, the XA_RETRY_ENTRY might be a good choice.  It doesn't normally
> > > > > appear in an XArray (it may appear if you're looking at a deleted node,
> > > > > but since we're holding the lock, we can't see deleted nodes).
> > > >
> > > ...
> > >
> > > > @@ -254,7 +267,7 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry)
> > > >  static void put_unlocked_entry(struct xa_state *xas, void *entry)
> > > >  {
> > > >       /* If we were the only waiter woken, wake the next one */
> > > > -     if (entry)
> > > > +     if (entry && dax_is_conflict(entry))
> > >
> > > This should be !dax_is_conflict(entry)...
> > >
> > > >               dax_wake_entry(xas, entry, false);
> > > >  }
> > >
> > > Otherwise the patch looks good to me so feel free to add:
> > >
> > > Reviewed-by: Jan Kara <jack@...e.cz>
> >
> > Looks good, and passes the test case. Now pushed out to
> > libnvdimm-for-next for v5.3 inclusion:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/commit/?h=libnvdimm-for-next&id=23c84eb7837514e16d79ed6d849b13745e0ce688
>
> Thanks for picking up the patch but you didn't apply the fix I've mentioned
> above. So put_unlocked_entry() is not waking up anybody anymore... Since
> this got already to Linus' tree, I guess a separate fixup patch is needed
> (attached).

Sigh, indeed. I think what happened is I applied the fixup locally,
tested it, and then later reapplied the patch from the list as I was
integrating the new automatic "Link:" generation script that has been
proposed on the ksummit list.

I'll get this pushed immediately.

Lesson learned: no manual local fixups, ask for resends to always be
able to pull the exact contents from the list.