[dm-devel] [PATCH] dax: fix for do not print error message for non-persistent memory block device

[John Pittman]

But it should be moved prior to the two bdev_dax_pgoff() checks right?
 Else a misaligned partition on a dax unsupported block device can
print the below messages.

kernel: sda1: error: unaligned partition for dax
kernel: sda2: error: unaligned partition for dax
kernel: sda3: error: unaligned partition for dax

Reviewed-by: John Pittman <jpittman at redhat.com>

On Thu, Sep 3, 2020 at 12:12 PM Coly Li <colyli at suse.de> wrote:
>
> On 2020/9/4 00:06, Ira Weiny wrote:
> > On Thu, Sep 03, 2020 at 07:55:49PM +0800, Coly Li wrote:
> >> When calling __generic_fsdax_supported(), a dax-unsupported device may
> >> not have dax_dev as NULL, e.g. the dax related code block is not enabled
> >> by Kconfig.
> >>
> >> Therefore in __generic_fsdax_supported(), to check whether a device
> >> supports DAX or not, the following order should be performed,
> >> - If dax_dev pointer is NULL, it means the device driver explicitly
> >>   announce it doesn't support DAX. Then it is OK to directly return
> >>   false from __generic_fsdax_supported().
> >> - If dax_dev pointer is NOT NULL, it might be because the driver doesn't
> >>   support DAX and not explicitly initialize related data structure. Then
> >>   bdev_dax_supported() should be called for further check.
> >>
> >> IMHO if device driver desn't explicitly set its dax_dev pointer to NULL,
> >> this is not a bug. Calling bdev_dax_supported() makes sure they can be
> >> recognized as dax-unsupported eventually.
> >>
> >> This patch does the following change for the above purpose,
> >>     -       if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
> >>     +       if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
> >>
> >>
> >> Fixes: c2affe920b0e ("dax: do not print error message for non-persistent memory block device")
> >> Signed-off-by: Coly Li <colyli at suse.de>
> >
> > I hate to do this because I realize this is a bug which people really need
> > fixed.
> >
> > However, shouldn't we also check (!dax_dev || !bdev_dax_supported()) as the
> > _first_ check in __generic_fsdax_supported()?
> >
> > It seems like the other pr_info's could also be called when DAX is not
> > supported and we probably don't want them to be?
> >
> > Perhaps that should be a follow on patch though.  So...
>
> I am not author of c2affe920b0e, but I guess it was because
> bdev_dax_supported() needed blocksize, so blocksize should pass previous
> checks firstly to make sure bdev_dax_supported() has a correct blocksize
> to check.
>
> >
> > As a direct fix to c2affe920b0e
> >
> > Reviewed-by: Ira Weiny <ira.weiny at intel.com>
>
> Thanks.
>
> Coly Li
>
>
> >
> >> Cc: Adrian Huang <ahuang12 at lenovo.com>
> >> Cc: Ira Weiny <ira.weiny at intel.com>
> >> Cc: Jan Kara <jack at suse.com>
> >> Cc: Mike Snitzer <snitzer at redhat.com>
> >> Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
> >> Cc: Vishal Verma <vishal.l.verma at intel.com>
> >> ---
> >>  drivers/dax/super.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> >> index 32642634c1bb..e5767c83ea23 100644
> >> --- a/drivers/dax/super.c
> >> +++ b/drivers/dax/super.c
> >> @@ -100,7 +100,7 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
> >>              return false;
> >>      }
> >>
> >> -    if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
> >> +    if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
> >>              pr_debug("%s: error: dax unsupported by block device\n",
> >>                              bdevname(bdev, buf));
> >>              return false;
> >> --
> >> 2.26.2
> >>
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