Re: [PATCH] drm/i915/gt: debugfs: Evaluate forcewake usage within locks

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On 6/11/2024 3:58 PM, Tvrtko Ursulin wrote:

On 10/06/2024 10:24, Nirmoy Das wrote:
Hi Andi,

On 6/7/2024 4:51 PM, Andi Shyti wrote:
The forcewake count and domains listing is multi process critical
and the uncore provides a spinlock for such cases.

Lock the forcewake evaluation section in the fw_domains_show()
debugfs interface.

Signed-off-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>

Needs a Fixes tag, below seems to be correct one.


Fixes: 9dd4b065446a ("drm/i915/gt: Move pm debug files into a gt aware debugfs")

Cc: <stable@xxxxxxxxxxxxxxx> # v5.6+

Reviewed-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>

What is the back story here and why would it need backporting? IGT cares about the atomic view of user_forcewake_count and individual domains or what?

There is no serious back story. This came from a static code analyzer report. I keep forgetting debugfs isn't mounted on production systems so we don't have to backport this patch.


Thanks,

Nirmoy


Regards,

Tvrtko



Regards,

Nirmoy


---
  drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
index 4fcba42cfe34..0437fd8217e0 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
@@ -71,6 +71,8 @@ static int fw_domains_show(struct seq_file *m, void *data)
      struct intel_uncore_forcewake_domain *fw_domain;
      unsigned int tmp;
+    spin_lock_irq(&uncore->lock);
+
      seq_printf(m, "user.bypass_count = %u\n",
             uncore->user_forcewake_count);
@@ -79,6 +81,8 @@ static int fw_domains_show(struct seq_file *m, void *data)
intel_uncore_forcewake_domain_to_str(fw_domain->id),
                 READ_ONCE(fw_domain->wake_count));
+    spin_unlock_irq(&uncore->lock);
+
      return 0;
  }
  DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(fw_domains);



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