From: Jani Nikula <jani.nikula@linux.intel.com>
To: DRI Development <dri-devel@lists.freedesktop.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
stable@vger.kernel.org, Jens Axboe <axboe@fb.com>,
Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH] drm: Fix locking for sysfs dpms file
Date: Tue, 29 Sep 2015 16:30:39 +0300 [thread overview]
Message-ID: <87bnclic8w.fsf@intel.com> (raw)
In-Reply-To: <1443513413-28873-1-git-send-email-daniel.vetter@ffwll.ch>
On Tue, 29 Sep 2015, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> With atomic drivers we need to make sure that (at least in general)
> property reads hold the right locks. But the legacy dpms property is
> special and can be read locklessly. Since userspace loves to just
> randomly look at that all the time (like with "status") do that.
>
> To make it clear that we play tricks use the READ_ONCE compiler
> barrier (and also for paranoia).
>
> Note that there's not really anything bad going on since even with the
> new atomic paths we eventually end up not chasing any pointers (and
> hence possibly freed memory and other fun stuff). The locking WARNING
> has been added in
>
> commit 88a48e297b3a3bac6022c03babfb038f1a886cea
> Author: Rob Clark <robdclark@gmail.com>
> Date: Thu Dec 18 16:01:50 2014 -0500
>
> drm: add atomic properties
>
> but since drivers are converting not everyone will have seen this from
> the start.
>
> Jens reported this and submitted a patch to just grab the
> mode_config.connection_mutex, but we can do a bit better.
>
> v2: Remove unused variables I failed to git add for real.
>
Reference: http://mid.gmane.org/20150928194822.GA3930@kernel.dk
> Reported-by: Jens Axboe <axboe@fb.com>
> Cc: Jens Axboe <axboe@fb.com>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
> drivers/gpu/drm/drm_sysfs.c | 12 +++---------
> 1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> index f08873f6489c..615b7e667320 100644
> --- a/drivers/gpu/drm/drm_sysfs.c
> +++ b/drivers/gpu/drm/drm_sysfs.c
> @@ -230,18 +230,12 @@ static ssize_t dpms_show(struct device *device,
> char *buf)
> {
> struct drm_connector *connector = to_drm_connector(device);
> - struct drm_device *dev = connector->dev;
> - uint64_t dpms_status;
> - int ret;
> + int dpms;
>
> - ret = drm_object_property_get_value(&connector->base,
> - dev->mode_config.dpms_property,
> - &dpms_status);
> - if (ret)
> - return 0;
> + dpms = READ_ONCE(connector->dpms);
>
> return snprintf(buf, PAGE_SIZE, "%s\n",
> - drm_get_dpms_name((int)dpms_status));
> + drm_get_dpms_name(dpms));
> }
>
> static ssize_t enabled_show(struct device *device,
> --
> 2.5.1
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Jani Nikula, Intel Open Source Technology Center
next prev parent reply other threads:[~2015-09-29 13:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-29 7:37 [PATCH] drm: Fix locking for sysfs dpms file Daniel Vetter
2015-09-29 7:56 ` Daniel Vetter
2015-09-29 13:30 ` Jani Nikula [this message]
2015-09-29 14:37 ` Jens Axboe
2015-09-29 8:06 ` [PATCH 1/3] drm/sysfs: Annote lockless show functions with READ_ONCE Daniel Vetter
2015-09-29 8:06 ` [PATCH 2/3] drm/sysfs: Grab lock for edid/modes_show Daniel Vetter
2015-10-02 8:39 ` [PATCH] " Daniel Vetter
2015-10-02 11:01 ` Daniel Vetter
2015-10-02 12:08 ` Emil Velikov
2015-11-19 16:22 ` Daniel Vetter
2015-10-02 15:02 ` Julia Lawall
2015-09-29 8:06 ` [PATCH 3/3] drm/sysfs: Nuke TV/DVI property files Daniel Vetter
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=87bnclic8w.fsf@intel.com \
--to=jani.nikula@linux.intel.com \
--cc=axboe@fb.com \
--cc=daniel.vetter@ffwll.ch \
--cc=daniel.vetter@intel.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=intel-gfx@lists.freedesktop.org \
--cc=stable@vger.kernel.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).