Monday, May 7, 2012, 3:28:36 PM, you wrote: > Hi, > On 05/07/2012 01:44 PM, Hans Verkuil wrote: >> On Monday 07 May 2012 13:06:01 Laurent Pinchart wrote: >>> Hi Sanser, >>> >>> On Sunday 06 May 2012 16:54:40 Sander Eikelenboom wrote: >>>> Hello Laurent / Mauro, >>>> >>>> I have updated to latest 3.4-rc5-tip, running multiple video grabbers. >>>> I don't see anything specific to uvcvideo anymore, but i do get the possible >>>> circular locking dependency below. >>> >>> Thanks for the report. >>> >>> We indeed have a serious issue there (CC'ing Hans Verkuil). >>> >>> Hans, serializing both ioctl handling an mmap with a single device lock as we >>> currently do in V4L2 is prone to AB-BA deadlocks (uvcvideo shouldn't be >>> affected as it has no device-wide lock). >>> >>> If we want to keep a device-wide lock we need to take it after the mm- >>>> mmap_sem lock in all code paths, as there's no way we can change the lock >>> ordering for mmap(). The copy_from_user/copy_to_user issue could be solved by >>> moving locking from v4l2_ioctl to __video_do_ioctl (device-wide locks would >>> then require using video_ioctl2), but I'm not sure whether that will play >>> nicely with the QBUF implementation in videobuf2 (which already includes a >>> workaround for this particular AB-BA deadlock issue). >> >> I've seen the same thing. It was on my TODO list of things to look into. I think >> mmap shouldn't take the device wide lock at all. But it will mean reviewing >> affected drivers before I can remove it. >> >> To be honest, I wasn't sure whether or not to take the device lock for mmap when >> I first wrote that code. >> >> If you look at irc I had a discussion today with HdG about adding flags to >> selectively disable locks for fops. It may be an idea to implement this soon so >> we can start updating drivers one-by-one. > I've a patch almost ready for this, when I'm happy with it I'll send of a new > version of the (ever growing) gspca use control framework patchset both me and > the other Hans have been working on, which will include this patch. Hi Hans, Is there any progress on this ? It still happens when booting with a 3.5-rc4 kernel. Probably with either the PWC or the em28xx driver. -- Sander > Regards, > Hans -- Best regards, Sander mailto:linux@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
