From: Dan Williams <dan.j.williams@intel.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>, Jan Kara <jack@suse.cz>,
stable <stable@vger.kernel.org>,
Robert Barror <robert.barror@intel.com>,
Seema Pandit <seema.pandit@intel.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] filesystem-dax: Disable PMD support
Date: Fri, 28 Jun 2019 09:39:01 -0700 [thread overview]
Message-ID: <CAPcyv4jeRwhYWnGw9RrfDA54RRa9LK4JPuF3zQ-av=HdRqCTJw@mail.gmail.com> (raw)
In-Reply-To: <20190628163721.GC4286@bombadil.infradead.org>
On Fri, Jun 28, 2019 at 9:37 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Jun 27, 2019 at 07:39:37PM -0700, Dan Williams wrote:
> > On Thu, Jun 27, 2019 at 12:59 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > On Thu, Jun 27, 2019 at 12:09:29PM -0700, Dan Williams wrote:
> > > > > This bug feels like we failed to unlock, or unlocked the wrong entry
> > > > > and this hunk in the bisected commit looks suspect to me. Why do we
> > > > > still need to drop the lock now that the radix_tree_preload() calls
> > > > > are gone?
> > > >
> > > > Nevermind, unmapp_mapping_pages() takes a sleeping lock, but then I
> > > > wonder why we don't restart the lookup like the old implementation.
> > >
> > > If something can remove a locked entry, then that would seem like the
> > > real bug. Might be worth inserting a lookup there to make sure that it
> > > hasn't happened, I suppose?
> >
> > Nope, added a check, we do in fact get the same locked entry back
> > after dropping the lock.
>
> Okay, good, glad to have ruled that out.
>
> > The deadlock revolves around the mmap_sem. One thread holds it for
> > read and then gets stuck indefinitely in get_unlocked_entry(). Once
> > that happens another rocksdb thread tries to mmap and gets stuck
> > trying to take the mmap_sem for write. Then all new readers, including
> > ps and top that try to access a remote vma, then get queued behind
> > that write.
> >
> > It could also be the case that we're missing a wake up.
>
> That was the conclusion I came to; that one thread holding the mmap sem
> for read isn't being woken up when it should be. Just need to find it ...
> obviously it's something to do with the PMD entries.
Can you explain to me one more time, yes I'm slow on the uptake on
this, the difference between xas_load() and xas_find_conflict() and
why it's ok for dax_lock_page() to use xas_load() while
grab_mapping_entry() uses xas_find_conflict()?
next prev parent reply other threads:[~2019-06-28 16:39 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 0:15 [PATCH] filesystem-dax: Disable PMD support Dan Williams
2019-06-27 12:34 ` Matthew Wilcox
2019-06-27 16:06 ` Dan Williams
2019-06-27 18:29 ` Dan Williams
2019-06-27 18:58 ` Dan Williams
2019-06-27 19:09 ` Dan Williams
2019-06-27 19:59 ` Matthew Wilcox
2019-06-28 2:39 ` Dan Williams
2019-06-28 16:37 ` Matthew Wilcox
2019-06-28 16:39 ` Dan Williams [this message]
2019-06-28 16:54 ` Matthew Wilcox
2019-06-29 16:03 ` Matthew Wilcox
2019-06-30 7:27 ` Dan Williams
2019-06-30 8:01 ` Dan Williams
2019-06-30 15:23 ` Matthew Wilcox
2019-06-30 21:37 ` Dan Williams
2019-07-02 3:34 ` Matthew Wilcox
2019-07-02 15:37 ` Dan Williams
2019-07-03 0:22 ` Boaz Harrosh
2019-07-03 0:42 ` Dan Williams
2019-07-03 1:39 ` Boaz Harrosh
2019-07-01 12:11 ` Jan Kara
2019-07-03 15:47 ` Matthew Wilcox
2019-07-04 16:40 ` Jan Kara
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