Re: [PATCH] pmem: report error on clear poison failure

[Ross Zwisler]

On Thu, Oct 13, 2016 at 06:16:29PM +0000, Kani, Toshimitsu wrote:
> On Thu, 2016-10-13 at 10:22 -0700, Dan Williams wrote:
> > On Thu, Oct 13, 2016 at 9:08 AM, Kani, Toshimitsu <toshi.kani@xxxxxxx
> > > wrote:
> > > 
> > > On Thu, 2016-10-13 at 09:01 -0700, Dan Williams wrote:
> > > > 
> > > > On Thu, Oct 13, 2016 at 8:54 AM, Toshi Kani <toshi.kani@xxxxxxx>
> > > > wrote:
> > > > > 
> > > > > 
> > > > > ACPI Clear Uncorrectable Error DSM function may fail or may be
> > > > > unsupported on a platform.  pmem_clear_poison() returns without
> > > > > clearing badblocks in such cases, which leads to a silent data
> > > > > corruption.
> > > > > 
> > > > > Change pmem_do_bvec() and pmem_clear_poison() to return -EIO
> > > > > so that filesystem can log an error message.
> > > > 
> > > > What's the silent data corruption scenario?  If the clear poison
> > > > fails I'm assuming that the poison will still be notified on the
> > > > next
> > > > read.
> > > 
> > > I agree that the data is eventually read, but there is no guranteed
> > > that when it is read soon enough, i.e. user might not access to the
> > > data for a long time.
> > 
> > ...but that's the same behavior for errors that we don't yet know
> > about.  That said, we indeed know that the write failed.  I'd feel
> > better about this patch if the justification / impact was clearer in
> > the changelog, because "silent data corruption" is not the impact.
> 
> Agreed.  How about the following descritpion?
> 
> ===
> ACPI Clear Uncorrectable Error DSM function may fail or may be
> unsupported on a platform.  pmem_clear_poison() returns without
> clearing badblocks in such cases.  This failure is detected at
> the next read (-EIO).
> 
> This behavior can lead to an issue when user keeps writing but
> does not read immedicately.  For instance, flight recorder file
		immediately

> may be only read when it is necessary for troubleshooting.
> 
> Change pmem_do_bvec() and pmem_clear_poison() to return -EIO
> so that filesystem can log an error message on a write error.
> ===
> 
> Thanks,
> -Toshi
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