Re: [PATCH v2] drm/i915: Fixup userptr mmu notifier registration error handling

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Oct 17, 2017 at 04:09:08PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> Avoid dereferencing the error pointer and also avoid returning NULL
> from i915_mmu_notifier_find since the callers do not expect that.

How did my patch return a NULL value? At least I assume that's the reasonf
for your v2 ...
-Daniel

> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Fixes: 7741b547b6e0 ("drm/i915: Preallocate our mmu notifier workequeu to unbreak cpu hotplug deadlock")
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_userptr.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index cdc9be799eee..e26b23171b56 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -221,15 +221,17 @@ i915_mmu_notifier_find(struct i915_mm_struct *mm)
>  			/* Protected by mm_lock */
>  			mm->mn = fetch_and_zero(&mn);
>  		}
> -	} else {
> -		/* someone else raced and successfully installed the mmu
> -		 * notifier, we can cancel our own errors */
> +	} else if (mm->mn) {
> +		/*
> +		 * Someone else raced and successfully installed the mmu
> +		 * notifier, we can cancel our own errors.
> +		 */
>  		err = 0;
>  	}
>  	mutex_unlock(&mm->i915->mm_lock);
>  	up_write(&mm->mm->mmap_sem);
>  
> -	if (mn) {
> +	if (mn && !IS_ERR(mn)) {
>  		destroy_workqueue(mn->wq);
>  		kfree(mn);
>  	}
> -- 
> 2.9.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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