Hi Mauro, On Thursday, 23 November 2017 15:07:51 EET Mauro Carvalho Chehab wrote: > Em Thu, 16 Nov 2017 02:33:48 +0200 Laurent Pinchart escreveu: > > Device unplug being asynchronous, it naturally races with operations > > performed by userspace through ioctls or other file operations on video > > device nodes. > > > > This leads to potential access to freed memory or to other resources > > during device access if unplug occurs during device access. To solve > > this, we need to wait until all device access completes when unplugging > > the device, and block all further access when the device is being > > unplugged. > > > > Three new functions are introduced. The video_device_enter() and > > video_device_exit() functions must be used to mark entry and exit from > > all code sections where the device can be accessed. The > > video_device_unplug() function is then used in the unplug handler to > > mark the device as being unplugged and wait for all access to complete. > > > > As an example mark the ioctl handler as a device access section. Other > > file operations need to be protected too, and blocking ioctls (such as > > VIDIOC_DQBUF) need to be handled as well. > > > > Signed-off-by: Laurent Pinchart > > <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > > --- > > > > drivers/media/v4l2-core/v4l2-dev.c | 57 +++++++++++++++++++++++++++++++++ > > include/media/v4l2-dev.h | 47 +++++++++++++++++++++++++++++++ > > 2 files changed, 104 insertions(+) [snip] > I'm c/c Greg here, as I don't think, that, the way it is, it > belongs at V4L2 core. > > I mean: if this is a problem that affects all drivers, it would should, > instead, be sitting at the driver's core. > > If, otherwise, this is specific to rcar-vin (and other platform drivers), > that's likely should be inside the drivers that require it. > > That's said, I remember we had to add some things in the past for > USB drivers hot unplug to happen softly. I don't remember the specifics > anymore, but it was solved by both a V4L2 core and changes at USB > drivers. > > One of the things that it was added, on that time, was this patch: > > commit ae6cfaace120f4330715b56265ce0e4a710e1276 > Author: Hans Verkuil <hverkuil@xxxxxxxxx> > Date: Sat Mar 14 08:28:45 2009 -0300 > > V4L/DVB (11044): v4l2-device: add v4l2_device_disconnect > > So, I would expect that a change at V4L2 core (or at driver core) that > would be applied would also be affecting USB drivers disconnect logic > and v4l2_device_disconnect() function. I wasn't aware of v4l2_device_disconnect(), thank you for pointing it out. I don't know what the full history behind that function is, but I don't see why it's needed. struct device instances are refcounted, the struct device corresponding to a USB device or USB interface doesn't get freed when a device is disconnected as long as a reference is present. We take such a reference in v4l2_device_register(), so there should be no problem. [snip] -- Regards, Laurent Pinchart
