From: "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>
To: Brian Starkey <Brian.Starkey@arm.com>
Cc: "Lowry Li (Arm Technology China)" <Lowry.Li@arm.com>,
Liviu Dudau <Liviu.Dudau@arm.com>,
"maarten.lankhorst@linux.intel.com"
<maarten.lankhorst@linux.intel.com>,
"seanpaul@chromium.org" <seanpaul@chromium.org>,
"airlied@linux.ie" <airlied@linux.ie>,
"daniel@ffwll.ch" <daniel@ffwll.ch>,
"Julien Yin (Arm Technology China)" <Julien.Yin@arm.com>,
"maxime.ripard@bootlin.com" <maxime.ripard@bootlin.com>,
"eric@anholt.net" <eric@anholt.net>,
"kieran.bingham+renesas@ideasonboard.com"
<kieran.bingham+renesas@ideasonboard.com>,
"sean@poorly.run" <sean@poorly.run>,
"laurent.pinchart@ideasonboard.com"
<laurent.pinchart@ideasonboard.com>,
"Jonathan Chai (Arm Technology China)" <Jonathan.Chai@arm.com>,
Ayan Halder <Ayan.Halder@arm.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>, nd <nd@arm.com>
Subject: Re: [PATCH v1 2/2] drm: Clear the fence pointer when writeback job signaled
Date: Fri, 2 Aug 2019 10:09:26 +0000 [thread overview]
Message-ID: <20190802100919.GA26225@jamwan02-TSP300> (raw)
In-Reply-To: <20190802092920.4la5cwrltv2m6dke@DESKTOP-E1NTVVP.localdomain>
On Fri, Aug 02, 2019 at 05:29:20PM +0800, Brian Starkey wrote:
> Hi Lowry,
>
> On Thu, Aug 01, 2019 at 06:34:08AM +0000, Lowry Li (Arm Technology China) wrote:
> > Hi Brian,
> >
> > On Wed, Jul 31, 2019 at 09:20:04PM +0800, Brian Starkey wrote:
> > > Hi Lowry,
> > >
> > > Thanks for this cleanup.
> > >
> > > On Wed, Jul 31, 2019 at 11:04:45AM +0000, Lowry Li (Arm Technology China) wrote:
> > > > During it signals the completion of a writeback job, after releasing
> > > > the out_fence, we'd clear the pointer.
> > > >
> > > > Check if fence left over in drm_writeback_cleanup_job(), release it.
> > > >
> > > > Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@arm.com>
> > > > ---
> > > > drivers/gpu/drm/drm_writeback.c | 23 +++++++++++++++--------
> > > > 1 file changed, 15 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> > > > index ff138b6..43d9e3b 100644
> > > > --- a/drivers/gpu/drm/drm_writeback.c
> > > > +++ b/drivers/gpu/drm/drm_writeback.c
> > > > @@ -324,6 +324,9 @@ void drm_writeback_cleanup_job(struct drm_writeback_job *job)
> > > > if (job->fb)
> > > > drm_framebuffer_put(job->fb);
> > > >
> > > > + if (job->out_fence)
> > >
> > > I'm thinking it might be a good idea to signal the fence with an error
> > > here, if it's not already signaled. Otherwise, if there's someone
> > > waiting (which there shouldn't be), they're going to be waiting a very
> > > long time :-)
> > >
> > > Thanks,
> > > -Brian
> > >
> > Here it happened at atomic_check failed and test only commit. For both
> > cases, the commit has been dropped and it's only a clean up. So here better
> > not be treated as an error case:)
>
> If anyone else has a reference on the fence, then IMO it absolutely is
> an error to reach this point without the fence being signaled -
> because it means that the fence will never be signaled.
>
> I don't think the API gives you a way to check if this is the last
> reference, so it's safest to just make sure the fence is signalled
> before dropping the reference.
>
> It just feels wrong to me to have the possibility of a dangling fence
> which is never going to get signalled; and it's an easy defensive step
> to make sure it can never happen.
>
> I know it _shouldn't_ happen, but we often put in handling for cases
> which shouldn't happen, because they frequently do happen :-)
>
> >
> > Since for userspace, it should have been failed or a test only case, so
> > writebace fence should not be signaled.
>
> It's not only userspace that can wait on fences (and in fact this
> fence will never even reach userspace if the commit fails), the driver
> may have taken a copy to use for "something".
>
Maybe we can add a wb_fence canceling into complete_signaling() for the
atomic_check failed cleanup like the crtc->out_fence.
Then if in this place we still can got a fence here, that must be a
error we signal and WARN it
Thanks
James
> Cheers,
> -Brian
>
> >
> > Best regards,
> > Lowry
> > > > + dma_fence_put(job->out_fence);
> > > > +
> > > > kfree(job);
> > > > }
> >
> > --
> > Regards
> > Lowry
next prev parent reply other threads:[~2019-08-02 10:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 11:04 [PATCH v1 0/2] Free the writeback_job when it with an empty fb Lowry Li (Arm Technology China)
2019-07-31 11:04 ` [PATCH v1 1/2] drm: " Lowry Li (Arm Technology China)
2019-07-31 13:03 ` Liviu Dudau
2019-09-23 7:24 ` [v1,1/2] " james qian wang (Arm Technology China)
2019-07-31 11:04 ` [PATCH v1 2/2] drm: Clear the fence pointer when writeback job signaled Lowry Li (Arm Technology China)
2019-07-31 13:15 ` Liviu Dudau
[not found] ` <20190801063055.GA17887@lowry.li@arm.com>
2019-08-01 9:58 ` Liviu Dudau
2019-07-31 13:20 ` Brian Starkey
[not found] ` <20190801063351.GB17887@lowry.li@arm.com>
2019-08-02 9:29 ` Brian Starkey
2019-08-02 9:43 ` Daniel Vetter
2019-08-02 9:45 ` Daniel Vetter
2019-08-02 10:09 ` Brian Starkey
2019-08-02 14:06 ` Daniel Vetter
2019-08-02 10:09 ` james qian wang (Arm Technology China) [this message]
2019-08-05 13:10 ` Brian Starkey
2019-09-23 7:25 ` [v1,2/2] " james qian wang (Arm Technology China)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190802100919.GA26225@jamwan02-TSP300 \
--to=james.qian.wang@arm.com \
--cc=Ayan.Halder@arm.com \
--cc=Brian.Starkey@arm.com \
--cc=Jonathan.Chai@arm.com \
--cc=Julien.Yin@arm.com \
--cc=Liviu.Dudau@arm.com \
--cc=Lowry.Li@arm.com \
--cc=airlied@linux.ie \
--cc=daniel@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=eric@anholt.net \
--cc=kieran.bingham+renesas@ideasonboard.com \
--cc=laurent.pinchart@ideasonboard.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-renesas-soc@vger.kernel.org \
--cc=maarten.lankhorst@linux.intel.com \
--cc=maxime.ripard@bootlin.com \
--cc=nd@arm.com \
--cc=sean@poorly.run \
--cc=seanpaul@chromium.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).