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.
Regards,
Nirmoy
Thanks,
Janusz
debug_object_activate(ref, &active_debug_desc);
}
