linux-kernel - Re: [PATCH v2 04/11] drm/qxl: fix lockdep issue in qxl_alloc_release

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Date:   Wed, 17 Feb 2021 20:23:30 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Gerd Hoffmann <kraxel@...hat.com>, dri-devel@...ts.freedesktop.org
Cc:     Dave Airlie <airlied@...hat.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/11] drm/qxl: fix lockdep issue in
 qxl_alloc_release_reserved



Am 17.02.21 um 13:32 schrieb Gerd Hoffmann:
> Call qxl_bo_unpin (which does a reservation) without holding the
> release_mutex lock.  Fixes lockdep (correctly) warning on a possible
> deadlock.
> 
> Fixes: 65ffea3c6e73 ("drm/qxl: unpin release objects")
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>

Acked-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
>   drivers/gpu/drm/qxl/qxl_release.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c
> index 716d706ca7f0..f5845c96d414 100644
> --- a/drivers/gpu/drm/qxl/qxl_release.c
> +++ b/drivers/gpu/drm/qxl/qxl_release.c
> @@ -283,7 +283,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
>   				       int type, struct qxl_release **release,
>   				       struct qxl_bo **rbo)
>   {
> -	struct qxl_bo *bo;
> +	struct qxl_bo *bo, *free_bo = NULL;
>   	int idr_ret;
>   	int ret = 0;
>   	union qxl_release_info *info;
> @@ -315,8 +315,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
>   
>   	mutex_lock(&qdev->release_mutex);
>   	if (qdev->current_release_bo_offset[cur_idx] + 1 >= releases_per_bo[cur_idx]) {
> -		qxl_bo_unpin(qdev->current_release_bo[cur_idx]);
> -		qxl_bo_unref(&qdev->current_release_bo[cur_idx]);
> +		free_bo = qdev->current_release_bo[cur_idx];
>   		qdev->current_release_bo_offset[cur_idx] = 0;
>   		qdev->current_release_bo[cur_idx] = NULL;
>   	}
> @@ -324,6 +323,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
>   		ret = qxl_release_bo_alloc(qdev, &qdev->current_release_bo[cur_idx], priority);
>   		if (ret) {
>   			mutex_unlock(&qdev->release_mutex);
> +			if (free_bo) {
> +				qxl_bo_unpin(free_bo);
> +				qxl_bo_unref(&free_bo);
> +			}
>   			qxl_release_free(qdev, *release);
>   			return ret;
>   		}
> @@ -339,6 +342,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
>   		*rbo = bo;
>   
>   	mutex_unlock(&qdev->release_mutex);
> +	if (free_bo) {
> +		qxl_bo_unpin(free_bo);
> +		qxl_bo_unref(&free_bo);
> +	}
>   
>   	ret = qxl_release_list_add(*release, bo);
>   	qxl_bo_unref(&bo);
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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