On Friday, 10 March 2023 17:48:10 CET Das, Nirmoy wrote:
> Hi Janusz,
>
> On 3/10/2023 4:19 PM, Janusz Krzysztofik wrote:
> > Hi Nirmoy,
> >
> > On Friday, 10 March 2023 15:11:38 CET Nirmoy Das wrote:
> >> debug_active_activate() expected ref->count to be zero
> >> which is not true anymore as __i915_active_activate() calls
> >> debug_active_activate() after incrementing the count.
> >>
> >> Fixes: 04240e30ed06 ("drm/i915: Skip taking acquire mutex for no ref-
>active
> > callback")
> >> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxx>
> >> Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> >> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> >> Cc: <stable@xxxxxxxxxxxxxxx> # v5.10+
> >> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> >> ---
> >> drivers/gpu/drm/i915/i915_active.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/
> > i915_active.c
> >> index a9fea115f2d2..1c3066eb359a 100644
> >> --- a/drivers/gpu/drm/i915/i915_active.c
> >> +++ b/drivers/gpu/drm/i915/i915_active.c
> >> @@ -92,7 +92,7 @@ static void debug_active_init(struct i915_active *ref)
> >> static void debug_active_activate(struct i915_active *ref)
> >> {
> >> lockdep_assert_held(&ref->tree_lock);
> >> - if (!atomic_read(&ref->count)) /* before the first inc */
> >> + if (atomic_read(&ref->count) == 1) /* after the first inc */
> > While that's obviously better than never calling debug_active_activate(),
I'm
> > wondering how likely we can still miss it because the counter being
> > incremented, e.g. via i915_active_acquire_if_busy(), by a concurrent
thread.
> > Since __i915_active_activate() is the only user and its decision making
step
> > is serialized against itself with a spinlock, couldn't we better call
> > debug_object_activate() unconditionally here?
>
>
> Yes, we can call debug_object_activate() without checking ref->count.
> Also we can remove the ref-count check for
>
> debug_active_deactivate() as this is wrapped with
> "atomic_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, flags)".
>
>
> I think it makes sense to keep this patch as it is so it can be
> backported easily. I can add another patch to remove
>
> unnecessary ref->count checks.
Looking at 5.10, I can't understand how dropping the check instead of
replacing it with a still problematic one could make backporting less easy.
Thanks,
Janusz
>
>
> Regards,
>
> Nirmoy
>
>
> >
> > Thanks,
> > Janusz
> >
> >> debug_object_activate(ref, &active_debug_desc);
> >> }
> >>
> >>
> >
> >
> >
>
