linux-kernel - Re: [PATCH] drm/ttm: fix double lock on glob->lru

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Date:   Fri, 22 Dec 2017 19:58:30 +0100
From:   Christian König <christian.koenig@....com>
To:     Colin King <colin.king@...onical.com>,
        Roger He <Hongbo.He@....com>, David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/ttm: fix double lock on glob->lru_lock

NAK,  ttm_bo_cleanup_refs() is dropping the lock.

Your backtrace is cause by an issue I've fixed this morning on 
amd-staging-drm-next.

Regards,
Christian.

Am 22.12.2017 um 19:03 schrieb Colin King:
> From: Colin Ian King <colin.king@...onical.com>
>
> Lock glob->lru_lock is locked before the while loop and also
> locked again at the end of the while loop; it appears that the
> lock at the end of the while loop is a double lock that should
> be removed.  CoverityScan picked this up with the introduction
> of the referenced commit inthe Fixes tag, however, it may have
> existed before this.  I've not been able to test this, but it
> does look incorrect to me.
>
> Detected by CoverityScan, CID#1268846 ("Double lock")
>
> Fixes: 827ed2b06b05 ("drm/ttm: use try_lock in ttm_bo_delayed_delete again")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>   drivers/gpu/drm/ttm/ttm_bo.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 60bb5c12b568..fb8d13a4bc94 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -595,7 +595,6 @@ static bool ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool remove_all)
>   		}
>   
>   		kref_put(&bo->list_kref, ttm_bo_release_list);
> -		spin_lock(&glob->lru_lock);
>   	}
>   	list_splice_tail(&removed, &bdev->ddestroy);
>   	empty = list_empty(&bdev->ddestroy);