linux-kernel - Re: [PATCH v7 1/2] drm/gem: Properly annotate WW context on drm_gem_lock

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Message-ID: <YvKOJRbTsBk91aPO@phenom.ffwll.local>
Date:   Tue, 9 Aug 2022 18:41:09 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     David Airlie <airlied@...ux.ie>, Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Christian König <christian.koenig@....com>,
        Thomas Hellström <thomas_os@...pmail.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        linux-tegra@...r.kernel.org, kernel@...labora.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v7 1/2] drm/gem: Properly annotate WW context on
 drm_gem_lock_reservations() error

On Thu, Jun 30, 2022 at 11:04:04PM +0300, Dmitry Osipenko wrote:
> Use ww_acquire_fini() in the error code paths. Otherwise lockdep
> thinks that lock is held when lock's memory is freed after the
> drm_gem_lock_reservations() error. The ww_acquire_context needs to be
> annotated as "released", which fixes the noisy "WARNING: held lock freed!"
> splat of VirtIO-GPU driver with CONFIG_DEBUG_MUTEXES=y and enabled lockdep.
> 
> Cc: stable@...r.kernel.org
> Fixes: 7edc3e3b975b5 ("drm: Add helpers for locking an array of BO reservations.")
> Reviewed-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

I merged this one to drm-misc-next-fixes. The other one looks like there's
still opens pending, pls resubmit appropriately (and maybe with some
analysis in the commit message of how exactly this impacts other drivers).
-Daniel

> ---
>  drivers/gpu/drm/drm_gem.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index eb0c2d041f13..86d670c71286 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1226,7 +1226,7 @@ drm_gem_lock_reservations(struct drm_gem_object **objs, int count,
>  		ret = dma_resv_lock_slow_interruptible(obj->resv,
>  								 acquire_ctx);
>  		if (ret) {
> -			ww_acquire_done(acquire_ctx);
> +			ww_acquire_fini(acquire_ctx);
>  			return ret;
>  		}
>  	}
> @@ -1251,7 +1251,7 @@ drm_gem_lock_reservations(struct drm_gem_object **objs, int count,
>  				goto retry;
>  			}
>  
> -			ww_acquire_done(acquire_ctx);
> +			ww_acquire_fini(acquire_ctx);
>  			return ret;
>  		}
>  	}
> -- 
> 2.36.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch