nvdimm.lists.linux.dev archive mirror
 help / color / mirror / Atom feed
From: Matthew Wilcox <willy@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Barret Rhoden <brho@google.com>, Jan Kara <jack@suse.cz>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH] dax: Fix deadlock in dax_lock_mapping_entry()
Date: Thu, 4 Oct 2018 19:52:12 -0700	[thread overview]
Message-ID: <20181005025212.GA12446@bombadil.infradead.org> (raw)
In-Reply-To: <CAPcyv4gf5MSaBnzFFrk4XG4OEJFTOqWshk-F==3=4GGMnwNtQw@mail.gmail.com>

On Thu, Oct 04, 2018 at 06:57:52PM -0700, Dan Williams wrote:
> On Thu, Oct 4, 2018 at 9:27 AM Jan Kara <jack@suse.cz> wrote:
> >
> > On Thu 27-09-18 11:22:22, Dan Williams wrote:
> > > On Thu, Sep 27, 2018 at 6:41 AM Jan Kara <jack@suse.cz> wrote:
> > > >
> > > > On Thu 27-09-18 06:28:43, Matthew Wilcox wrote:
> > > > > On Thu, Sep 27, 2018 at 01:23:32PM +0200, Jan Kara wrote:
> > > > > > When dax_lock_mapping_entry() has to sleep to obtain entry lock, it will
> > > > > > fail to unlock mapping->i_pages spinlock and thus immediately deadlock
> > > > > > against itself when retrying to grab the entry lock again. Fix the
> > > > > > problem by unlocking mapping->i_pages before retrying.
> > > > >
> > > > > It seems weird that xfstests doesn't provoke this ...
> > > >
> > > > The function currently gets called only from mm/memory-failure.c. And yes,
> > > > we are lacking DAX hwpoison error tests in fstests...
> > >
> > > I have an item on my backlog to port the ndctl unit test that does
> > > memory_failure() injection vs ext4 over to fstests. That said I've
> > > been investigating a deadlock on ext4 caused by this test. When I saw
> > > this patch I hoped it was root cause, but the test is still failing
> > > for me. Vishal is able to pass the test on his system, so the failure
> > > mode is timing dependent. I'm running this patch on top of -rc5 and
> > > still seeing the following deadlock.
> >
> > I went through the code but I don't see where the problem could be. How can
> > I run that test? Is KVM enough or do I need hardware with AEP dimms?
> 
> KVM is enough... however, I have found a hack that makes the test pass:
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 52517f28e6f4..d7f035b1846e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1668,6 +1668,9 @@ unsigned find_get_entries(struct address_space *mapping,
>                         goto repeat;
>                 }
>  export:
> +               if (iter.index < start)
> +                       continue;
> +
>                 indices[ret] = iter.index;
>                 entries[ret] = page;
>                 if (++ret == nr_entries)
> 
> Is this a radix bug? I would never expect:
> 
>     radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start)
> 
> ...to return entries with an index < start. Without that change above
> we loop forever because dax_layout_busy_page() can't make forward
> progress. I'll dig into the radix code tomorrow, but maybe someone
> else will be me to it overnight.

If 'start' is within a 2MB entry, iter.index can absolutely be less
than start.  I forget exactly what the radix tree code does, but I think
it returns index set to the canonical/base index of the entry.
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

  reply	other threads:[~2018-10-05  2:52 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-27 11:23 Jan Kara
2018-09-27 13:28 ` Matthew Wilcox
2018-09-27 13:41   ` Jan Kara
2018-09-27 18:22     ` Dan Williams
2018-10-04 16:27       ` Jan Kara
2018-10-05  1:57         ` Dan Williams
2018-10-05  2:52           ` Matthew Wilcox [this message]
2018-10-05  4:01             ` Dan Williams
2018-10-05  4:28               ` Dan Williams
2018-10-05  9:54                 ` Jan Kara
2018-10-06 18:04                   ` Dan Williams

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181005025212.GA12446@bombadil.infradead.org \
    --to=willy@infradead.org \
    --cc=brho@google.com \
    --cc=dan.j.williams@intel.com \
    --cc=jack@suse.cz \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-nvdimm@lists.01.org \
    --subject='Re: [PATCH] dax: Fix deadlock in dax_lock_mapping_entry()' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).