[Intel-xe] [PATCH] drm/xe: Fix lockdep warning in xe_force_wake calls

[Matthew Brost]

On Fri, Nov 10, 2023 at 11:59:07AM +0530, Aravind Iddamsetty wrote:
> Use spin_lock_irqsave, spin_unlock_irqrestore
> 
> Fix for below:
> [13994.811263] ========================================================
> [13994.811295] WARNING: possible irq lock inversion dependency detected
> [13994.811326] 6.6.0-rc3-xe #2 Tainted: G     U
> [13994.811358] --------------------------------------------------------
> [13994.811388] swapper/0/0 just changed the state of lock:
> [13994.811416] ffff895c7e044db8 (&cpuctx_lock){-...}-{2:2}, at:
> __perf_event_read+0xb7/0x3a0
> [13994.811494] but this lock took another, HARDIRQ-unsafe lock in the
> past:
> [13994.811528]  (&fw->lock){+.+.}-{2:2}
> [13994.811544]
> 
>                and interrupts could create inverse lock ordering between
> them.
> 
> [13994.811606]
>                other info that might help us debug this:
> [13994.811636]  Possible interrupt unsafe locking scenario:
> 
> [13994.811667]        CPU0                    CPU1
> [13994.811691]        ----                    ----
> [13994.811715]   lock(&fw->lock);
> [13994.811744]                                local_irq_disable();
> [13994.811773]                                lock(&cpuctx_lock);
> [13994.811810]                                lock(&fw->lock);
> [13994.811846]   <Interrupt>
> [13994.811865]     lock(&cpuctx_lock);
> [13994.811895]
>                 *** DEADLOCK ***
> 

I don't personally like this. Where in an irq context do we grab this
lock? FW probably shouldn't ever be grabbed from an irq context. I see
this was changed from a mutex to spin lock in which is pretty suspect
IMO.

'drm/xe: Use spinlock in forcewake instead of mutex'  

If this really needs to be a spin lock I'd rather have versions of
xe_force_wake_get/put that called from non-atomic contexts (e.g. use
spin_lock_irq) and atomic contexts (e.g. use spin_lock) rather than
using spin_lock_irqsave.

Matt

> Cc: Anshuman Gupta <anshuman.gupta at intel.com>
> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty at linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_force_wake.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_force_wake.c b/drivers/gpu/drm/xe/xe_force_wake.c
> index 32d6c4dd2807..9bbe8a5040da 100644
> --- a/drivers/gpu/drm/xe/xe_force_wake.c
> +++ b/drivers/gpu/drm/xe/xe_force_wake.c
> @@ -145,9 +145,10 @@ int xe_force_wake_get(struct xe_force_wake *fw,
>  	struct xe_gt *gt = fw_to_gt(fw);
>  	struct xe_force_wake_domain *domain;
>  	enum xe_force_wake_domains tmp, woken = 0;
> +	unsigned long flags;
>  	int ret, ret2 = 0;
>  
> -	spin_lock(&fw->lock);
> +	spin_lock_irqsave(&fw->lock, flags);
>  	for_each_fw_domain_masked(domain, domains, fw, tmp) {
>  		if (!domain->ref++) {
>  			woken |= BIT(domain->id);
> @@ -162,7 +163,7 @@ int xe_force_wake_get(struct xe_force_wake *fw,
>  				   domain->id, ret);
>  	}
>  	fw->awake_domains |= woken;
> -	spin_unlock(&fw->lock);
> +	spin_unlock_irqrestore(&fw->lock, flags);
>  
>  	return ret2;
>  }
> @@ -174,9 +175,10 @@ int xe_force_wake_put(struct xe_force_wake *fw,
>  	struct xe_gt *gt = fw_to_gt(fw);
>  	struct xe_force_wake_domain *domain;
>  	enum xe_force_wake_domains tmp, sleep = 0;
> +	unsigned long flags;
>  	int ret, ret2 = 0;
>  
> -	spin_lock(&fw->lock);
> +	spin_lock_irqsave(&fw->lock, flags);
>  	for_each_fw_domain_masked(domain, domains, fw, tmp) {
>  		if (!--domain->ref) {
>  			sleep |= BIT(domain->id);
> @@ -191,7 +193,7 @@ int xe_force_wake_put(struct xe_force_wake *fw,
>  				   domain->id, ret);
>  	}
>  	fw->awake_domains &= ~sleep;
> -	spin_unlock(&fw->lock);
> +	spin_unlock_irqrestore(&fw->lock, flags);
>  
>  	return ret2;
>  }
> -- 
> 2.25.1
>