Re: dm-integrity: revert adc0daad366b to fix recalculation

[Mike Snitzer <snitzer@redhat.com>]

On Wed, Jul 22 2020 at  2:46pm -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> Hi Mike
> 
> Please submit this to Linus and to RHEL-8.
> 
> Mikulas
> 
> 
> 
> From: Mikulas Patocka <mpatocka@redhat.com>
> 
> The patch adc0daad366b62ca1bce3e2958a40b0b71a8b8b3 broke recalculation on
> dm-integrity. The patch replaces a private variable "suspending" with a
> call to "dm_suspended".
> 
> The problem is that dm_suspended returns true not only during suspend, but
> also during resume. This race condition could occur:
> 1. dm_integrity_resume calls queue_work(ic->recalc_wq, &ic->recalc_work)
> 2. integrity_recalc (&ic->recalc_work) preempts the current thread
> 3. integrity_recalc calls if (unlikely(dm_suspended(ic->ti))) goto unlock_ret;
> 4. integrity_recalc exits and no recalculating is done.
> 
> In order to fix this race condition, we stop using dm_suspended and start
> using the variable "suspending" (that is only set during suspend, not
> during resume).
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Fixes: adc0daad366b ("dm: report suspended device during destroy")
> Cc: stable@vger.kernel.org	# v4.18+

OK, but why not add a dm_suspending() to DM core?  Could be other
future targets would like this same info right?  I don't see harm in
elevating it.

Mike