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@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: Thomas Hellström thomas.hellstrom@intel.com Cc: Andi Shyti andi.shyti@linux.intel.com Cc: intel-gfx@lists.freedesktop.org Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Nirmoy Das nirmoy.das@intel.com
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);}