From: Rob Clark <robdclark@gmail.com>
To: Hillf Danton <hdanton@sina.com>, Rob Clark <robdclark@gmail.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
Rob Clark <robdclark@chromium.org>, Sean Paul <sean@poorly.run>,
David Airlie <airlied@linux.ie>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 13/14] drm/msm: Drop struct_mutex in shrinker path
Date: Mon, 5 Oct 2020 09:49:37 -0700 [thread overview]
Message-ID: <CAF6AEGveqvvv9MfBMAr34y9664fPouGjwPrK=v9OLVXv4dHzxg@mail.gmail.com> (raw)
In-Reply-To: <20201005140203.GS438822@phenom.ffwll.local>
On Mon, Oct 5, 2020 at 7:02 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Mon, Oct 05, 2020 at 05:24:19PM +0800, Hillf Danton wrote:
> >
> > On Sun, 4 Oct 2020 12:21:45
> > > From: Rob Clark <robdclark@chromium.org>
> > >
> > > Now that the inactive_list is protected by mm_lock, and everything
> > > else on per-obj basis is protected by obj->lock, we no longer depend
> > > on struct_mutex.
> > >
> > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > ---
> > > drivers/gpu/drm/msm/msm_gem.c | 1 -
> > > drivers/gpu/drm/msm/msm_gem_shrinker.c | 54 --------------------------
> > > 2 files changed, 55 deletions(-)
> > >
> > [...]
> >
> > > @@ -71,13 +33,8 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> > > {
> > > struct msm_drm_private *priv =
> > > container_of(shrinker, struct msm_drm_private, shrinker);
> > > - struct drm_device *dev = priv->dev;
> > > struct msm_gem_object *msm_obj;
> > > unsigned long freed = 0;
> > > - bool unlock;
> > > -
> > > - if (!msm_gem_shrinker_lock(dev, &unlock))
> > > - return SHRINK_STOP;
> > >
> > > mutex_lock(&priv->mm_lock);
> >
> > Better if the change in behavior is documented that SHRINK_STOP will
> > no longer be needed.
>
> btw I read through this and noticed you have your own obj lock, plus
> mutex_lock_nested. I strongly recommend to just cut over to dma_resv_lock
> for all object lock needs (soc drivers have been terrible with this
> unfortuntaly), and in the shrinker just use dma_resv_trylock instead of
> trying to play clever games outsmarting lockdep.
>
> I recently wrote an entire blog length rant on why I think
> mutex_lock_nested is too dangerous to be useful:
>
> https://blog.ffwll.ch/2020/08/lockdep-false-positives.html
>
> Not anything about this here, just general comment. The problem extends to
> shmem helpers and all that also having their own locks for everything.
the shrinker lock class has existed for a while.. and is based on the
idea that anything in the get-pages/vmap path cannot happen on a
WONTNEED bo.. although perhaps there should be a few more 'if
(WARN_ON(obj->madv != WILLNEED)) return -EBUSY'..
replacing obj->lock with dma_resv lock, might be a nice cleanup.. but
I think it will be a bit churny..
BR,
-R
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
next prev parent reply other threads:[~2020-10-05 16:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-04 19:21 [PATCH 00/14] drm/msm: de-struct_mutex-ification Rob Clark
2020-10-04 19:21 ` [PATCH 01/14] drm/msm: Use correct drm_gem_object_put() in fail case Rob Clark
2020-10-04 19:21 ` [PATCH 02/14] drm/msm: Drop chatty trace Rob Clark
2020-10-05 14:15 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 03/14] drm/msm: Move update_fences() Rob Clark
2020-10-05 14:16 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 04/14] drm/msm: Add priv->mm_lock to protect active/inactive lists Rob Clark
2020-10-04 22:15 ` Daniel Vetter
2020-10-05 0:10 ` Rob Clark
2020-10-05 14:19 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 05/14] drm/msm: Document and rename preempt_lock Rob Clark
2020-10-05 14:22 ` Jordan Crouse
2020-10-04 19:21 ` [PATCH 06/14] drm/msm: Protect ring->submits with it's own lock Rob Clark
2020-10-05 14:23 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 07/14] drm/msm: Refcount submits Rob Clark
2020-10-05 13:56 ` Daniel Vetter
2020-10-05 16:24 ` Rob Clark
2020-10-05 14:27 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 08/14] drm/msm: Remove obj->gpu Rob Clark
2020-10-05 14:28 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 09/14] drm/msm: Drop struct_mutex from the retire path Rob Clark
2020-10-05 14:29 ` [Freedreno] " Jordan Crouse
2020-10-04 19:21 ` [PATCH 10/14] drm/msm: Drop struct_mutex in free_object() path Rob Clark
2020-10-04 19:21 ` [PATCH 11/14] drm/msm: remove msm_gem_free_work Rob Clark
2020-10-04 19:21 ` [PATCH 12/14] drm/msm: drop struct_mutex in madvise path Rob Clark
2020-10-04 19:21 ` [PATCH 13/14] drm/msm: Drop struct_mutex in shrinker path Rob Clark
2020-10-04 19:21 ` [PATCH 14/14] drm/msm: Don't implicit-sync if only a single ring Rob Clark
[not found] ` <20201005092419.15608-1-hdanton@sina.com>
2020-10-05 14:02 ` [PATCH 13/14] drm/msm: Drop struct_mutex in shrinker path Daniel Vetter
2020-10-05 16:17 ` Kristian Høgsberg
[not found] ` <20201006004416.15040-1-hdanton@sina.com>
2020-10-06 3:40 ` Rob Clark
2020-10-06 9:35 ` Daniel Vetter
2020-10-05 16:49 ` Rob Clark [this message]
2020-10-05 18:18 ` Daniel Vetter
2020-10-05 16:24 ` [Freedreno] [PATCH 00/14] drm/msm: de-struct_mutex-ification Kristian Høgsberg
2020-10-05 18:20 ` Daniel Vetter
2020-10-06 3:25 ` Rob Clark
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