Re: [PATCH] fix random failures in shell/integrity.sh

[Mikulas Patocka <mpatocka@redhat.com>]

On Thu, 7 Aug 2025, John Stoffel wrote:

> >>>>> "Mikulas" == Mikulas Patocka <mpatocka@redhat.com> writes:
> 
> > On Thu, 7 Aug 2025, Stuart D Gathman wrote:
> 
> >> On Wed, 6 Aug 2025, John Stoffel wrote:
> >> 
> >> > > > > > > "Mikulas" == Mikulas Patocka <mpatocka@redhat.com> writes:
> >> > 
> >> > > The problem is that the raid1 implementation may freely choose which leg
> >> > > to read from. If it chooses to read from the non-corrupted leg, the
> >> > > corruption is not detected, the number of mismatches is not incremented
> >> > > and the test reports this as a failure.
> >> > 
> >> > So wait, how is integrity supposed to work in this situation then?  In
> >> > real life?  I understand the test is hard, maybe doing it in a loop
> >> > three times?  Or configure the RAID1 to prefer one half over another
> >> > is the way to make this test work?
> 
> > If you want to make sure that you detect (and correct) all mismatches, you 
> > have to scrub the raid array.
> 
> And how do you know which level of the array is showing the errors?  I
> could have a RAID1 array composed of a single partition on the left
> side, but then a RAID0 of two smaller disks on the right side.  So how
> would this read() flag know what to do?  
> 
> I would assume the integrity sub-system would be reading from both
> sides and comparing them to look for errors.  When you find a
> mis-match, how do you tell which side is wrong?  

If you use dm-integrity on the raid legs (as it was done in this test), 
you know which leg is corrupted - dm-integrity will turn silent data 
corruptions into -EILSEQ.

So, all you have to do, is to initiate scrub on the array.

Mikulas