Den 01.04.2019 09.12, skrev Daniel Vetter:
> On Sat, Mar 30, 2019 at 10:07:58PM +0100, Noralf Trønnes wrote:
>>
>>
>> Den 28.03.2019 09.17, skrev Daniel Vetter:
>>> On Tue, Mar 26, 2019 at 06:55:43PM +0100, Noralf Trønnes wrote:
>>>> drm_fb_helper_is_bound() is used to check if DRM userspace is in control.
>>>> This is done by looking at the fb on the primary plane. By the time
>>>> fb-helper gets around to committing, it's possible that the facts have
>>>> changed.
>>>>
>>>> Avoid this race by holding the drm_device->master_mutex lock while
>>>> committing. When DRM userspace does its first open, it will now wait
>>>> until fb-helper is done. The helper will stay away if there's a master.
>>>>
>>>> Locking rule: Always take the fb-helper lock first.
>>>>
>>>> Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>>>> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
>>>
>>> I think it'd be good to reorder this earlier in the series. And I'm
>>> wondering why you didn't replace all occurences of the _is_bound()
>>> function. With the consistent master state check we're doing with this I
>>> don't think any of the fbdev checking is still needed. Plus looking at
>>> crtc->primary->fb without any locks is racy, so would be good to ditch
>>> that hack.
>>
>> _is_bound() is used in drm_fb_helper_hotplug_event() to decide on
>> delayed hotplug. The master lock won't help here. I have studied
>> drm_fb_helper for 2 years now, and I still think it is convoluted and
>> difficult to grasp in places. So I kept this one call site. I'm vary of
>> making unrelated changes in this series.
>
> Hm, why would it not work for the hotplug case? _is_bound already checks
> dev->master (but with races, unlike this here). And the other checks are
> various levels of cargo-culting. dev->master is (well, has become through
> retrofitting) the "who owns the display" tracking, I think fully
> standardizing on that makes sense. The only case where there's a
> difference is if:
> - some compositor dropped master
> - but didn't disable it's framebuffers
> We actually want that for smooth vt switching, so that the new compositor
> could take over in a transition. Having a special case with fbdev where
> the compositor has to disable all its fb or fbcon won't take over feels a
> bit irky.
You're right ofc.
I read '->deferred_setup = true' when in fact it is '->delayed_hotplug =
true', so I assumed there was something that _is_bound() was protecting
wrt. to setup state.
I'll fix it in the next version.
Noralf.
> -Daniel
>
>> The reason I included this patch is because it's used with the
>> bootsplash example support code. I can move the patch earlier in the series.
>>
>> Noralf.
>>
>>> -Daniel
>>>
>>>> ---
>>>> drivers/gpu/drm/drm_auth.c | 20 ++++++++++++++
>>>> drivers/gpu/drm/drm_fb_helper.c | 49 ++++++++++++++++++++++++---------
>>>> drivers/gpu/drm/drm_internal.h | 2 ++
>>>> 3 files changed, 58 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
>>>> index 1669c42c40ed..db199807b7dc 100644
>>>> --- a/drivers/gpu/drm/drm_auth.c
>>>> +++ b/drivers/gpu/drm/drm_auth.c
>>>> @@ -368,3 +368,23 @@ void drm_master_put(struct drm_master **master)
>>>> *master = NULL;
>>>> }
>>>> EXPORT_SYMBOL(drm_master_put);
>>>> +
>>>> +/* Used by drm_client and drm_fb_helper */
>>>> +bool drm_master_internal_acquire(struct drm_device *dev)
>>>> +{
>>>> + mutex_lock(&dev->master_mutex);
>>>> + if (dev->master) {
>>>> + mutex_unlock(&dev->master_mutex);
>>>> + return false;
>>>> + }
>>>> +
>>>> + return true;
>>>> +}
>>>> +EXPORT_SYMBOL(drm_master_internal_acquire);
>>>> +
>>>> +/* Used by drm_client and drm_fb_helper */
>>>> +void drm_master_internal_release(struct drm_device *dev)
>>>> +{
>>>> + mutex_unlock(&dev->master_mutex);
>>>> +}
>>>> +EXPORT_SYMBOL(drm_master_internal_release);
>>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>>>> index 4a073cd4e423..9f253fcf3f79 100644
>>>> --- a/drivers/gpu/drm/drm_fb_helper.c
>>>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>>>> @@ -41,6 +41,8 @@
>>>> #include <drm/drm_crtc_helper.h>
>>>> #include <drm/drm_atomic.h>
>>>>
>>>> +#include "drm_internal.h"
>>>> +
>>>> static bool drm_fbdev_emulation = true;
>>>> module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600);
>>>> MODULE_PARM_DESC(fbdev_emulation,
>>>> @@ -235,7 +237,12 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
>>>> return 0;
>>>>
>>>> mutex_lock(&fb_helper->lock);
>>>> - ret = drm_client_modesets_commit(fb_helper->dev, fb_helper->modesets);
>>>> + if (drm_master_internal_acquire(fb_helper->dev)) {
>>>> + ret = drm_client_modesets_commit(fb_helper->dev, fb_helper->modesets);
>>>> + drm_master_internal_release(fb_helper->dev);
>>>> + } else {
>>>> + ret = -EBUSY;
>>>> + }
>>>>
>>>> do_delayed = fb_helper->delayed_hotplug;
>>>> if (do_delayed)
>>>> @@ -332,13 +339,16 @@ static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { };
>>>> static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
>>>> {
>>>> struct drm_fb_helper *fb_helper = info->par;
>>>> + struct drm_device *dev = fb_helper->dev;
>>>>
>>>> /*
>>>> * For each CRTC in this fb, turn the connectors on/off.
>>>> */
>>>> mutex_lock(&fb_helper->lock);
>>>> - if (drm_fb_helper_is_bound(fb_helper))
>>>> - drm_client_modesets_dpms(fb_helper->dev, fb_helper->modesets, dpms_mode);
>>>> + if (drm_master_internal_acquire(dev)) {
>>>> + drm_client_modesets_dpms(dev, fb_helper->modesets, dpms_mode);
>>>> + drm_master_internal_release(dev);
>>>> + }
>>>> mutex_unlock(&fb_helper->lock);
>>>> }
>>>>
>>>> @@ -1097,6 +1107,7 @@ static int setcmap_atomic(struct fb_cmap *cmap, struct fb_info *info)
>>>> int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>>>> {
>>>> struct drm_fb_helper *fb_helper = info->par;
>>>> + struct drm_device *dev = fb_helper->dev;
>>>> int ret;
>>>>
>>>> if (oops_in_progress)
>>>> @@ -1104,9 +1115,9 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>>>>
>>>> mutex_lock(&fb_helper->lock);
>>>>
>>>> - if (!drm_fb_helper_is_bound(fb_helper)) {
>>>> + if (!drm_master_internal_acquire(dev)) {
>>>> ret = -EBUSY;
>>>> - goto out;
>>>> + goto unlock;
>>>> }
>>>>
>>>> if (info->fix.visual == FB_VISUAL_TRUECOLOR)
>>>> @@ -1116,7 +1127,8 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>>>> else
>>>> ret = setcmap_legacy(cmap, info);
>>>>
>>>> -out:
>>>> + drm_master_internal_release(dev);
>>>> +unlock:
>>>> mutex_unlock(&fb_helper->lock);
>>>>
>>>> return ret;
>>>> @@ -1136,11 +1148,13 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
>>>> unsigned long arg)
>>>> {
>>>> struct drm_fb_helper *fb_helper = info->par;
>>>> + struct drm_device *dev = fb_helper->dev;
>>>> struct drm_crtc *crtc;
>>>> int ret = 0;
>>>>
>>>> mutex_lock(&fb_helper->lock);
>>>> - if (!drm_fb_helper_is_bound(fb_helper)) {
>>>> +
>>>> + if (!drm_master_internal_acquire(dev)) {
>>>> ret = -EBUSY;
>>>> goto unlock;
>>>> }
>>>> @@ -1177,13 +1191,15 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
>>>> }
>>>>
>>>> ret = 0;
>>>> - goto unlock;
>>>> + break;
>>>> default:
>>>> ret = -ENOTTY;
>>>> }
>>>>
>>>> + drm_master_internal_release(dev);
>>>> unlock:
>>>> mutex_unlock(&fb_helper->lock);
>>>> +
>>>> return ret;
>>>> }
>>>> EXPORT_SYMBOL(drm_fb_helper_ioctl);
>>>> @@ -1426,15 +1442,19 @@ int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
>>>> return -EBUSY;
>>>>
>>>> mutex_lock(&fb_helper->lock);
>>>> - if (!drm_fb_helper_is_bound(fb_helper)) {
>>>> - mutex_unlock(&fb_helper->lock);
>>>> - return -EBUSY;
>>>> +
>>>> + if (!drm_master_internal_acquire(dev)) {
>>>> + ret = -EBUSY;
>>>> + goto unlock;
>>>> }
>>>>
>>>> if (drm_drv_uses_atomic_modeset(dev))
>>>> ret = pan_display_atomic(var, info);
>>>> else
>>>> ret = pan_display_legacy(var, info);
>>>> +
>>>> + drm_master_internal_release(dev);
>>>> +unlock:
>>>> mutex_unlock(&fb_helper->lock);
>>>>
>>>> return ret;
>>>> @@ -1451,6 +1471,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>>>> int ret = 0;
>>>> int crtc_count = 0;
>>>> struct drm_connector_list_iter conn_iter;
>>>> + struct drm_device *dev = fb_helper->dev;
>>>> struct drm_fb_helper_surface_size sizes;
>>>> struct drm_connector *connector;
>>>> struct drm_mode_set *mode_set;
>>>> @@ -1593,8 +1614,10 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>>>> DRM_INFO("Cannot find any crtc or sizes\n");
>>>>
>>>> /* First time: disable all crtc's.. */
>>>> - if (!fb_helper->deferred_setup && !READ_ONCE(fb_helper->dev->master))
>>>> - drm_client_modesets_commit(fb_helper->dev, fb_helper->modesets);
>>>> + if (!fb_helper->deferred_setup && drm_master_internal_acquire(dev)) {
>>>> + drm_client_modesets_commit(dev, fb_helper->modesets);
>>>> + drm_master_internal_release(dev);
>>>> + }
>>>> return -EAGAIN;
>>>> }
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
>>>> index 251d67e04c2d..6d5d1184c084 100644
>>>> --- a/drivers/gpu/drm/drm_internal.h
>>>> +++ b/drivers/gpu/drm/drm_internal.h
>>>> @@ -91,6 +91,8 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
>>>> struct drm_file *file_priv);
>>>> int drm_master_open(struct drm_file *file_priv);
>>>> void drm_master_release(struct drm_file *file_priv);
>>>> +bool drm_master_internal_acquire(struct drm_device *dev);
>>>> +void drm_master_internal_release(struct drm_device *dev);
>>>>
>>>> /* drm_sysfs.c */
>>>> extern struct class *drm_class;
>>>> --
>>>> 2.20.1
>>>>
>>>
>
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