RE: [External] Re: flood of "dm-X: error: dax access failed" due to 5.9 commit 231609785cbfb

[Adrian Huang12 <ahuang12@lenovo.com>]

> -----Original Message-----
> From: Coly Li <colyli@suse.de>
> Sent: Thursday, September 3, 2020 4:37 PM
> To: Mike Snitzer <snitzer@redhat.com>
> Cc: Jan Kara <jack@suse.com>; Ira Weiny <ira.weiny@intel.com>; Pankaj Gupta
> <pankaj.gupta.linux@gmail.com>; Vishal Verma <vishal.l.verma@intel.com>;
> linux-nvdimm@lists.01.org; Adrian Huang12 <ahuang12@lenovo.com>
> Subject: [External] Re: flood of "dm-X: error: dax access failed" due to 5.9
> commit 231609785cbfb
> 
> On 2020/9/3 13:20, Coly Li wrote:
> > On 2020/9/3 00:51, Mike Snitzer wrote:
> >> On Wed, Sep 02 2020 at 12:46pm -0400, Coly Li <colyli@suse.de> wrote:
> >>
> >>> On 2020/9/3 00:44, Mike Snitzer wrote:
> >>>> On Wed, Sep 02 2020 at 12:40pm -0400, Coly Li <colyli@suse.de>
> >>>> wrote:
> >>>>
> >>>>> On 2020/9/3 00:04, Mike Snitzer wrote:
> >>>>>> 5.9 commit 231609785cbfb ("dax: print error message by pr_info()
> >>>>>> in
> >>>>>> __generic_fsdax_supported()") switched from pr_debug() to pr_info().
> >>>>>>
> >>>>>> The justification in the commit header is really inadequate.  If
> >>>>>> there is a problem that you need to drill in on, repeat the
> >>>>>> testing after enabling the dynamic debugging.
> >>>>>>
> >>>>>> Otherwise, now all DM devices that aren't layered on DAX capable
> >>>>>> devices spew really confusing noise to users when they simply
> >>>>>> activate their non-DAX DM devices:
> >>>>>>
> >>>>>> [66567.129798] dm-6: error: dax access failed (-5) [66567.134400]
> >>>>>> dm-6: error: dax access failed (-5) [66567.139152] dm-6: error:
> >>>>>> dax access failed (-5) [66567.314546] dm-2: error: dax access
> >>>>>> failed (-95) [66567.319380] dm-2: error: dax access failed (-95)
> >>>>>> [66567.324254] dm-2: error: dax access failed (-95)
> >>>>>> [66567.479025] dm-2: error: dax access failed (-95)
> >>>>>> [66567.483713] dm-2: error: dax access failed (-95)
> >>>>>> [66567.488722] dm-2: error: dax access failed (-95)
> >>>>>> [66567.494061] dm-2: error: dax access failed (-95)
> >>>>>> [66567.498823] dm-2: error: dax access failed (-95)
> >>>>>> [66567.503693] dm-2: error: dax access failed (-95)
> >>>>>>
> >>>>>> commit 231609785cbfb must be reverted.
> >>>>>>
> >>>>>> Please advise, thanks.
> >>>>>
> >>>>> Adrian Huang from Lenovo posted a patch, which titled: dax: do not
> >>>>> print error message for non-persistent memory block device
> >>>>>
> >>>>> It fixes the issue, but no response for now. Maybe we should take this fix.
> >>>>
> >>>> OK, yes sounds like it.  It was merged and is commit
> >>>> c2affe920b0e066
> >>>> ("dax: do not print error message for non-persistent memory block
> >>>> device")
> >>>
> >>> Thanks for informing me this patch is merged, I am going to update
> >>> my local one :-)
> >>
> >> So the thing is I'm running v5.9-rc3 (which includes this commit) but
> >> I'm still seeing all these warnings when I run the lvm2 testsuite.
> >> The reason _seems_ to be because the lvm2 testsuite uses brd devices
> >> for test devices.  So there is something about the brd device that
> >> shows commit c2affe920b0e066 isn't enough :(
> >
> > [Resend and CC Adrian Huang]
> >
> > Hi Mike,
> >
> > Could you please apply and test this attached patch based on v5.9-rc3 ?
> >
> > It seems the pointer dax_dev of __generic_fsdax_supported() parameter
> > is not initialized (IMHO this is not a dm bug), therefore the &&
> > should be
> > || to check the dax support state.
> >
> > Also I add two pr_info() to print the variables value, let's see
> > whether my guess makes sense.
> 
> Also I suggest some kind of change like this in drivers/md/dm.c,
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c index
> fb0255d25e4b..566d8208df47 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -818,6 +818,8 @@ int dm_get_table_device(struct mapped_device *md,
> dev_t dev, fmode_t mode,
>                         return -ENOMEM;
>                 }
> 
> +               memset(td, 0, sizeof(struct table_device));
> +

This does not help. See the following log.

-----------------
# lvm2-testsuite --only activate-minor
.......
[ 0:00] #activate-minor.sh:22+ aux prepare_vg 2
[ 0:00] ## preparing ramdisk device...ok (/dev/ram0)
[ 0:01] 6,3160,150710756,-;brd: module loaded
[ 0:01] ## preparing 2 devices...ok
[ 0:01] 6,3161,150730864,-;dax_dev: 0000000000000000
[ 0:01] 6,3162,150730866,-;bdev_dax_supported(): 0
[ 0:01] 6,3163,150730903,-;dax_dev: 0000000000000000
[ 0:01] 6,3164,150730905,-;bdev_dax_supported(): 0
[ 0:01] 6,3165,150731019,-;dax_dev: 0000000000000000
[ 0:01] 6,3166,150731020,-;bdev_dax_supported(): 0
[ 0:01] 6,3167,150731512,-;dax_dev: 0000000000000000
[ 0:01] 6,3168,150731514,-;bdev_dax_supported(): 0
[ 0:01] 6,3169,150731525,-;dax_dev: 0000000000000000
[ 0:01] 6,3170,150731525,-;bdev_dax_supported(): 0
[ 0:01] 6,3171,150731656,-;dax_dev: 0000000000000000
[ 0:01] 6,3172,150731657,-;bdev_dax_supported(): 0
.......
[ 0:01] lvchange $vg/foo -a y
[ 0:01] #activate-minor.sh:25+ lvchange LVMTEST12302vg/foo -a y
[ 0:01]   /tmp/LVMTEST12302.W0HGxyzxst/dev/mapper/LVMTEST12302vg-foo not set up by udev: Falling back to direct node creation.
[ 0:01] 6,3173,150927070,-;dax_dev: 00000000f0a5865d
[ 0:01] 6,3174,150927072,-;bdev_dax_supported(): 0
[ 0:01] 6,3175,150927081,-;dax_dev: 00000000f0a5865d
[ 0:01] 6,3176,150927082,-;bdev_dax_supported(): 0
[ 0:01] 6,3177,150927241,-;dax_dev: 00000000f0a5865d
[ 0:01] 6,3178,150927242,-;bdev_dax_supported(): 0
----------------

>                 td->dm_dev.mode = mode;
>                 td->dm_dev.bdev = NULL;
> 
> 
> The above change may make sure *dax_dev sent into
> __generic_fsdax_supported() is always NULL if the target does not support DAX.
> But IMHO this is not 100% necessary, it just make
> __generic_fsdax_supported() return false faster by the following change in
> previous attached patch,
> 
>  -       if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
>  +       if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
> 
> I am not very familiar with dm code, CMIIW, just for your information.
> 
> Coly Li

-- Adrian
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