[Intel-gfx] [PATCH] drm/probe-helper: don't lose hotplug event
Rob Clark
robdclark at gmail.com
Sun Jan 25 09:37:31 PST 2015
On Wed, Jan 21, 2015 at 4:40 PM, Rob Clark <robdclark at gmail.com> wrote:
> On Wed, Jan 21, 2015 at 9:41 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>> There's a race window (small for hpd, 10s large for polled outputs)
>> where userspace could sneak in with an unrelated connnector probe
>> ioctl call and eat the hotplug event (since neither the hpd nor the
>> poll code see a state change).
>>
>> To avoid this, check whether the connector state changes in all other
>> ->detect calls (in the current helper code that's only probe_single)
>> and if that's the case, fire off a hotplug event. Note that we can't
>> directly call the hotplug event handler, since that expects that no
>> locks are held (due to reentrancy with the fb code to update the kms
>> console).
>>
>> Also, this requires that drivers using the probe_single helper
>> function set up the poll work. All current drivers do that already,
>> and with the reworked hpd handling there'll be no downside to
>> unconditionally setting up the poll work any more.
>>
>> v2: Review from Rob Clark
>> - Don't bail out of the output poll work immediately if it's disabled
>> to make sure we deliver the delayed hoptplug events. Instead just
>> jump to the tail.
>> - Don't scheduel the work when it's not set up. Would be a driver bug
>> since using probe helpers for anything dynamic without them
>> initialized makes them all noops.
>>
>> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> (v1)
>> Cc: Rob Clark <robdclark at gmail.com>
>> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> Reviewed-by: Rob Clark <robdclark at gmail.com>
>
> and with the monitor that started all this, plus the addition of:
> http://lists.freedesktop.org/archives/dri-devel/2015-January/075901.html
>
> Tested-by: Rob Clark <robdclark at gmail.com>
bleh, but on latest upstream (plus drm-next, etc).. possibly just not
caught earlier due to insufficient debug stuff enabled..
I could probably solve this by moving drm_kms_helper_poll_init()
earlier.. otoh that might cause other surprises and other drivers also
seem to do this late in their load..
[ 4.053197] WARNING: CPU: 3 PID: 52 at ../kernel/workqueue.c:1427
__queue_delayed_work+0x14c/0x15c()
[ 4.058040] Modules linked in:
[ 4.070017] CPU: 3 PID: 52 Comm: kworker/u8:1 Tainted: G U
3.19.0-rc5-00821-g415f9e0-dirty #1113
[ 4.070107] Hardware name: Qualcomm (Flattened Device Tree)
[ 4.080016] Workqueue: deferwq deferred_probe_work_func
[ 4.090549] [<c021654c>] (unwind_backtrace) from [<c0211f68>]
(show_stack+0x10/0x14)
[ 4.090714] [<c0211f68>] (show_stack) from [<c091d3bc>]
(dump_stack+0x8c/0x9c)
[ 4.098519] [<c091d3bc>] (dump_stack) from [<c0246a2c>]
(warn_slowpath_common+0x84/0xb4)
[ 4.105547] [<c0246a2c>] (warn_slowpath_common) from [<c0246af8>]
(warn_slowpath_null+0x1c/0x24)
[ 4.113790] [<c0246af8>] (warn_slowpath_null) from [<c0259b5c>]
(__queue_delayed_work+0x14c/0x15c)
[ 4.122556] [<c0259b5c>] (__queue_delayed_work) from [<c0259bbc>]
(queue_delayed_work_on+0x50/0x5c)
[ 4.131337] [<c0259bbc>] (queue_delayed_work_on) from [<c0561114>]
(drm_helper_probe_single_connector_modes_merge_bits+0x2fc/0x49c)
[ 4.140290] [<c0561114>]
(drm_helper_probe_single_connector_modes_merge_bits) from [<c0569824>]
(drm_fb_helper_probe_connector_modes.isra.5+0x4c/0x6c)
[ 4.152089] [<c0569824>]
(drm_fb_helper_probe_connector_modes.isra.5) from [<c056a8a8>]
(drm_fb_helper_initial_config+0x34/0x3d8)
[ 4.165624] [<c056a8a8>] (drm_fb_helper_initial_config) from
[<c05a62dc>] (msm_fbdev_init+0x70/0xa0)
[ 4.177342] [<c05a62dc>] (msm_fbdev_init) from [<c05a1614>]
(msm_load+0x268/0x36c)
[ 4.186537] [<c05a1614>] (msm_load) from [<c0573af4>]
(drm_dev_register+0xa8/0x104)
[ 4.193912] [<c0573af4>] (drm_dev_register) from [<c05759dc>]
(drm_platform_init+0x44/0xd8)
[ 4.201475] [<c05759dc>] (drm_platform_init) from [<c05c1654>]
(try_to_bring_up_master.part.3+0xc8/0x108)
[ 4.209804] [<c05c1654>] (try_to_bring_up_master.part.3) from
[<c05c1740>] (component_master_add_with_match+0xac/0x124)
[ 4.219525] [<c05c1740>] (component_master_add_with_match) from
[<c05a116c>] (msm_pdev_probe+0x64/0x70)
[ 4.230116] [<c05a116c>] (msm_pdev_probe) from [<c05c73c8>]
(platform_drv_probe+0x44/0xa4)
[ 4.239485] [<c05c73c8>] (platform_drv_probe) from [<c05c5c48>]
(driver_probe_device+0x108/0x23c)
[ 4.247813] [<c05c5c48>] (driver_probe_device) from [<c05c42ac>]
(bus_for_each_drv+0x64/0x98)
[ 4.256752] [<c05c42ac>] (bus_for_each_drv) from [<c05c5b10>]
(device_attach+0x74/0x88)
[ 4.265259] [<c05c5b10>] (device_attach) from [<c05c51fc>]
(bus_probe_device+0x84/0xa8)
[ 4.273071] [<c05c51fc>] (bus_probe_device) from [<c05c561c>]
(deferred_probe_work_func+0x64/0x94)
[ 4.281064] [<c05c561c>] (deferred_probe_work_func) from
[<c025a354>] (process_one_work+0x134/0x334)
[ 4.290091] [<c025a354>] (process_one_work) from [<c025ac30>]
(worker_thread+0x4c/0x4b0)
[ 4.299383] [<c025ac30>] (worker_thread) from [<c025ecfc>]
(kthread+0xdc/0xf4)
[ 4.307459] [<c025ecfc>] (kthread) from [<c020e978>]
(ret_from_fork+0x14/0x3c)
BR,
-R
>
>> ---
>> drivers/gpu/drm/drm_probe_helper.c | 36 ++++++++++++++++++++++++++++++++++--
>> include/drm/drm_crtc.h | 1 +
>> 2 files changed, 35 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
>> index 2fbdcca7ca9a..33bf550a1d3f 100644
>> --- a/drivers/gpu/drm/drm_probe_helper.c
>> +++ b/drivers/gpu/drm/drm_probe_helper.c
>> @@ -103,6 +103,7 @@ static int drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
>> int count = 0;
>> int mode_flags = 0;
>> bool verbose_prune = true;
>> + enum drm_connector_status old_status;
>>
>> WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
>>
>> @@ -121,7 +122,33 @@ static int drm_helper_probe_single_connector_modes_merge_bits(struct drm_connect
>> if (connector->funcs->force)
>> connector->funcs->force(connector);
>> } else {
>> + old_status = connector->status;
>> +
>> connector->status = connector->funcs->detect(connector, true);
>> +
>> + /*
>> + * Normally either the driver's hpd code or the poll loop should
>> + * pick up any changes and fire the hotplug event. But if
>> + * userspace sneaks in a probe, we might miss a change. Hence
>> + * check here, and if anything changed start the hotplug code.
>> + */
>> + if (old_status != connector->status) {
>> + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %d to %d\n",
>> + connector->base.id,
>> + connector->name,
>> + old_status, connector->status);
>> +
>> + /*
>> + * The hotplug event code might call into the fb
>> + * helpers, and so expects that we do not hold any
>> + * locks. Fire up the poll struct instead, it will
>> + * disable itself again.
>> + */
>> + dev->mode_config.delayed_event = true;
>> + if (dev->mode_config.poll_enabled)
>> + schedule_delayed_work(&dev->mode_config.output_poll_work,
>> + 0);
>> + }
>> }
>>
>> /* Re-enable polling in case the global poll config changed. */
>> @@ -274,10 +301,14 @@ static void output_poll_execute(struct work_struct *work)
>> struct drm_device *dev = container_of(delayed_work, struct drm_device, mode_config.output_poll_work);
>> struct drm_connector *connector;
>> enum drm_connector_status old_status;
>> - bool repoll = false, changed = false;
>> + bool repoll = false, changed;
>> +
>> + /* Pick up any changes detected by the probe functions. */
>> + changed = dev->mode_config.delayed_event;
>> + dev->mode_config.delayed_event = false;
>>
>> if (!drm_kms_helper_poll)
>> - return;
>> + goto out;
>>
>> mutex_lock(&dev->mode_config.mutex);
>> list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
>> @@ -319,6 +350,7 @@ static void output_poll_execute(struct work_struct *work)
>>
>> mutex_unlock(&dev->mode_config.mutex);
>>
>> +out:
>> if (changed)
>> drm_kms_helper_hotplug_event(dev);
>>
>> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
>> index f444263055c5..65da9fb939a7 100644
>> --- a/include/drm/drm_crtc.h
>> +++ b/include/drm/drm_crtc.h
>> @@ -1089,6 +1089,7 @@ struct drm_mode_config {
>> /* output poll support */
>> bool poll_enabled;
>> bool poll_running;
>> + bool delayed_event;
>> struct delayed_work output_poll_work;
>>
>> /* pointers to standard properties */
>> --
>> 2.1.4
>>
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