Re: [PATCH v3] drm/i915/gt: Use spin_lock_irqsave() in interruptible context

[Maciej Patelczyk <maciej.patelczyk@intel.com>]

On 16.01.2025 11:40, Krzysztof Karas wrote:

> spin_lock/unlock() functions used in interrupt contexts could
> result in a deadlock, as seen in GitLab issue #13399:
> https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13399,
> which occurs when interrupt comes in while holding a lock.
>
> Try to remedy the problem by saving irq state before spin lock
> acquisition.
>
> v2: add irqs' state save/restore calls to all locks/unlocks in
>   signal_irq_work() execution (Maciej)
>
> v3: use with spin_lock_irqsave() in guc_lrc_desc_unpin() instead
>   of other lock/unlock calls and add Fixes and Cc tags (Tvrtko);
>   change title and commit message
>
> Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
> Fixes: 2f2cc53b5fe7 ("drm/i915/guc: Close deregister-context race against CT-loss")
> Cc: <stable@vger.kernel.org> # v6.9+
> ---
>   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 12f1ba7ca9c1..29d9c81473cc 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -3433,10 +3433,10 @@ static inline int guc_lrc_desc_unpin(struct intel_context *ce)
>   	 */
>   	ret = deregister_context(ce, ce->guc_id.id);
>   	if (ret) {
> -		spin_lock(&ce->guc_state.lock);
> +		spin_lock_irqsave(&ce->guc_state.lock, flags);
>   		set_context_registered(ce);
>   		clr_context_destroyed(ce);
> -		spin_unlock(&ce->guc_state.lock);
> +		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>   		/*
>   		 * As gt-pm is awake at function entry, intel_wakeref_put_async merely decrements
>   		 * the wakeref immediately but per function spec usage call this after unlock.

Looked at this and wasn't seeing it. There is spin_lock_irqsave() used 
earlier.

Reviewed-by: Maciej Patelczyk <maciej.patelczyk@intel.com>