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Subject: Re: [PATCH v2 04/11] drm/qxl: fix lockdep issue in
 qxl_alloc_release_reserved
To:     Gerd Hoffmann <kraxel@redhat.com>, dri-devel@lists.freedesktop.org
Cc:     Dave Airlie <airlied@redhat.com>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@lists.linux-foundation.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20210217123213.2199186-1-kraxel@redhat.com>
 <20210217123213.2199186-5-kraxel@redhat.com>
From:   Thomas Zimmermann <tzimmermann@suse.de>
Message-ID: <8957d006-c521-292b-0e95-066098ec8b90@suse.de>
Date:   Wed, 17 Feb 2021 20:23:30 +0100
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From: Thomas Zimmermann <tzimmermann@suse.de>
To: Gerd Hoffmann <kraxel@redhat.com>, dri-devel@lists.freedesktop.org
Cc: Dave Airlie <airlied@redhat.com>, David Airlie <airlied@linux.ie>,
 Daniel Vetter <daniel@ffwll.ch>,
 "open list:DRM DRIVER FOR QXL VIRTUAL GPU"
 <virtualization@lists.linux-foundation.org>,
 "open list:DRM DRIVER FOR QXL VIRTUAL GPU"
 <spice-devel@lists.freedesktop.org>, open list <linux-kernel@vger.kernel.org>
Message-ID: <8957d006-c521-292b-0e95-066098ec8b90@suse.de>
Subject: Re: [PATCH v2 04/11] drm/qxl: fix lockdep issue in
 qxl_alloc_release_reserved
References: <20210217123213.2199186-1-kraxel@redhat.com>
 <20210217123213.2199186-5-kraxel@redhat.com>
In-Reply-To: <20210217123213.2199186-5-kraxel@redhat.com>

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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.
>=20
> Fixes: 65ffea3c6e73 ("drm/qxl: unpin release objects")
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

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

> ---
>   drivers/gpu/drm/qxl/qxl_release.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>=20
> diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qx=
l_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 *q=
dev, unsigned long size,
>   				       int type, struct qxl_release **release,
>   				       struct qxl_bo **rbo)
>   {
> -	struct qxl_bo *bo;
> +	struct qxl_bo *bo, *free_bo =3D NULL;
>   	int idr_ret;
>   	int ret =3D 0;
>   	union qxl_release_info *info;
> @@ -315,8 +315,7 @@ int qxl_alloc_release_reserved(struct qxl_device *q=
dev, unsigned long size,
>  =20
>   	mutex_lock(&qdev->release_mutex);
>   	if (qdev->current_release_bo_offset[cur_idx] + 1 >=3D releases_per_b=
o[cur_idx]) {
> -		qxl_bo_unpin(qdev->current_release_bo[cur_idx]);
> -		qxl_bo_unref(&qdev->current_release_bo[cur_idx]);
> +		free_bo =3D qdev->current_release_bo[cur_idx];
>   		qdev->current_release_bo_offset[cur_idx] =3D 0;
>   		qdev->current_release_bo[cur_idx] =3D NULL;
>   	}
> @@ -324,6 +323,10 @@ int qxl_alloc_release_reserved(struct qxl_device *=
qdev, unsigned long size,
>   		ret =3D qxl_release_bo_alloc(qdev, &qdev->current_release_bo[cur_id=
x], 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 =3D bo;
>  =20
>   	mutex_unlock(&qdev->release_mutex);
> +	if (free_bo) {
> +		qxl_bo_unpin(free_bo);
> +		qxl_bo_unref(&free_bo);
> +	}
>  =20
>   	ret =3D qxl_release_list_add(*release, bo);
>   	qxl_bo_unref(&bo);
>=20

--=20
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 N=C3=BCrnberg, Germany
(HRB 36809, AG N=C3=BCrnberg)
Gesch=C3=A4ftsf=C3=BChrer: Felix Imend=C3=B6rffer


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