linux-nvdimm.lists.01.org archive mirror
 help / color / mirror / Atom feed
From: Jan Kara <jack@suse.cz>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>, linux-nvdimm <linux-nvdimm@lists.01.org>,
	Adrian Huang <adrianhuang0701@gmail.com>,
	Coly Li <colyli@suse.de>, Mikulas Patocka <mpatocka@redhat.com>,
	Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>
Subject: Re: [PATCH] dm: Call proper helper to determine dax support
Date: Thu, 17 Sep 2020 12:42:16 +0200	[thread overview]
Message-ID: <20200917104216.GB16097@quack2.suse.cz> (raw)
In-Reply-To: <CAPcyv4gfMY=k+SDsKWPPasZs9X=7schOgc=3VZSDj0kAbZcTTA@mail.gmail.com>

On Thu 17-09-20 02:28:57, Dan Williams wrote:
> On Wed, Sep 16, 2020 at 8:15 AM Jan Kara <jack@suse.cz> wrote:
> >
> > DM was calling generic_fsdax_supported() to determine whether a device
> > referenced in the DM table supports DAX. However this is a helper for "leaf" device drivers so that
> > they don't have to duplicate common generic checks. High level code
> > should call dax_supported() helper which that calls into appropriate
> > helper for the particular device. This problem manifested itself as
> > kernel messages:
> >
> > dm-3: error: dax access failed (-95)
> >
> > when lvm2-testsuite run in cases where a DM device was stacked on top of
> > another DM device.
> >
> > Fixes: 7bf7eac8d648 ("dax: Arrange for dax_supported check to span multiple devices")
> > Tested-by: Adrian Huang <ahuang12@lenovo.com>
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  drivers/dax/super.c   |  4 ++++
> >  drivers/md/dm-table.c |  3 +--
> >  include/linux/dax.h   | 11 +++++++++--
> >  3 files changed, 14 insertions(+), 4 deletions(-)
> >
> > This patch should go in together with Adrian's
> > https://lore.kernel.org/linux-nvdimm/20200916133923.31-1-adrianhuang0701@gmail.com
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index e5767c83ea23..b6284c5cae0a 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -325,11 +325,15 @@ EXPORT_SYMBOL_GPL(dax_direct_access);
> >  bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
> >                 int blocksize, sector_t start, sector_t len)
> >  {
> > +       if (!dax_dev)
> > +               return false;
> > +
> 
> Hi Jan, Thanks for this.
> 
> >         if (!dax_alive(dax_dev))
> >                 return false;
> 
> One small fixup to quiet lockdep because dax_supported() calls
> dax_alive() it expects that dax_read_lock() is held. So I'm testing
> with this incremental change:
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index bed1ff0744ec..229f461e7def 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -860,9 +860,14 @@ EXPORT_SYMBOL_GPL(dm_table_set_type);
>  int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
>                         sector_t start, sector_t len, void *data)
>  {
> -       int blocksize = *(int *) data;
> +       int blocksize = *(int *) data, id;
> +       bool rc;
> 
> -       return dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
> +       id = dax_read_lock();
> +       rc = dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
> +       dax_read_unlock(id);
> +
> +       return rc;
>  }

Yeah, thanks for this! I was actually looking into this when writing the
patch and somehow convinced myself we will always be called through
bdev_dax_supported() which does dax_read_lock() for us. But apparently I
was wrong...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org

  reply	other threads:[~2020-09-17 10:42 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-16 15:14 Jan Kara
2020-09-16 15:22 ` Mike Snitzer
2020-09-17  8:08   ` Jan Kara
2020-09-17  9:28 ` [PATCH] " Dan Williams
2020-09-17 10:42   ` Jan Kara [this message]
2020-09-17 14:57     ` Huang Adrian
2020-09-17 15:03       ` Huang Adrian
2020-09-17 17:49       ` Dan Williams
2020-09-18  5:41         ` Dan Williams
2020-09-18 12:41           ` Huang Adrian
2020-09-18 12:48             ` Huang Adrian
2020-09-18 20:12             ` Dan Williams
2020-09-18 12:34         ` Huang Adrian

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=20200917104216.GB16097@quack2.suse.cz \
    --to=jack@suse.cz \
    --cc=adrianhuang0701@gmail.com \
    --cc=agk@redhat.com \
    --cc=colyli@suse.de \
    --cc=dan.j.williams@intel.com \
    --cc=linux-nvdimm@lists.01.org \
    --cc=mpatocka@redhat.com \
    --cc=snitzer@redhat.com \
    --subject='Re: [PATCH] dm: Call proper helper to determine dax support' \
    /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
on how to clone and mirror all data and code used for this inbox