[PATCH] modesetting: Fix X crash in ms_dirty_update()

[jimqu]

在 2018/8/3 23:08, Michel Dänzer 写道:
> On 2018-08-03 03:27 PM, Jim Qu wrote:
>> On some Intel iGPU + AMD dGPU platform, when connect extern display
>> from dGPU, X will crash, show the log like:
>>
>> randr: falling back to unsynchronized pixmap sharing
>> (EE)
>> (EE) Backtrace:
>> (EE) 0: /usr/lib/xorg/Xorg (xorg_backtrace+0x4e)
>> (EE) 1: /usr/lib/xorg/Xorg (0x55cb0151a000+0x1b5ce9)
>> (EE) 2: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7f1587a1d000+0x11390)
>> (EE)
>> (EE) Segmentation fault at address 0x0
>> (EE)
>>
>> There is NULL pointer accessing on ent->slave_dst->drawable.pScreen->
>> SharedPixmapNotifyDamage.
>>
>> On the platform, since the dGPU is GPU device, so that the iGPU is
>> output master device. SharedPixmapNotifyDamage() should be called when
>> current device is output slave.
>>
>> Change-Id: Id633e29c126670ee64ff1f5f79d489e5068cd439
>> Signed-off-by: Jim Qu <Jim.Qu at amd.com>
>> ---
>>   hw/xfree86/drivers/modesetting/driver.c | 23 ++++++++++++-----------
>>   1 file changed, 12 insertions(+), 11 deletions(-)
>>
>> diff --git a/hw/xfree86/drivers/modesetting/driver.c b/hw/xfree86/drivers/modesetting/driver.c
>> index 9362370..6022315 100644
>> --- a/hw/xfree86/drivers/modesetting/driver.c
>> +++ b/hw/xfree86/drivers/modesetting/driver.c
>> @@ -640,20 +640,21 @@ ms_dirty_update(ScreenPtr screen, int *timeout)
>>       xorg_list_for_each_entry(ent, &screen->pixmap_dirty_list, ent) {
>>           region = DamageRegion(ent->damage);
>>           if (RegionNotEmpty(region)) {
>> -            msPixmapPrivPtr ppriv =
>> -                msGetPixmapPriv(&ms->drmmode, ent->slave_dst);
>> +            if (screen->isGPU) {
>> +                msPixmapPrivPtr ppriv =
>> +                    msGetPixmapPriv(&ms->drmmode, ent->slave_dst);
>>   
>> -            if (ppriv->notify_on_damage) {
>> -                ppriv->notify_on_damage = FALSE;
>> +                if (ppriv->notify_on_damage) {
>> +                    ppriv->notify_on_damage = FALSE;
>>   
>> -                ent->slave_dst->drawable.pScreen->
>> -                    SharedPixmapNotifyDamage(ent->slave_dst);
>> -            }
>> -
>> -            /* Requested manual updating */
>> -            if (ppriv->defer_dirty_update)
>> -                continue;
>> +                    ent->slave_dst->drawable.pScreen->
>> +                        SharedPixmapNotifyDamage(ent->slave_dst);
>> +                }
>>   
>> +                /* Requested manual updating */
>> +                if (ppriv->defer_dirty_update)
>> +                    continue;
>> +            }
> I don't think this is right. E.g. why would the slave driver call its
> own SharedPixmapNotifyDamage hook? Also, ppriv->defer_dirty_update is
> only set to TRUE by hooks which are only called for the master screen.
>
> So, I think the start of the new block needs to be something like:
>
>              if (!screen->isGPU) {
>                  msPixmapPrivPtr ppriv =
>                      msGetPixmapPriv(&ms->drmmode,
> ent->slave_dst->master_pixmap);

Indeed, you are right, current modsetting driver should be as output 
source(master screen), and it call slave's SharedPixmapNotifyDamage() to 
present shared buffer. I will update in the next version.

> and msStartFlippingPixmapTracking and msStopFlippingPixmapTracking also
> need to use ->master_pixmap instead of the slave pixmaps.
>
>
> Not sure about the defer_dirty_update related code, that might only make
> sense in the slave.
>
>
> The more I look at this PRIME synchronization related code, the more I
> wonder if it was ever tested with master and slave screens using
> different drivers...

Yeah,  Maybe , the master hook PresentSharedPixmap() also need master 
pixmap.

Thanks
JimQu
>
>