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    SubjectRe: BUG: unable to handle kernel paging request at 6b6b6bcb (v4l2_device_disconnect+0x11/0x30)
    Date
    On Monday, September 05, 2011 11:59:03 Laurent Pinchart wrote:
    > Hi Hans,
    >
    > On Friday 02 September 2011 09:29:08 Sitsofe Wheeler wrote:
    > > On Fri, Sep 02, 2011 at 01:35:49PM +0800, Dave Young wrote:
    > > > On Fri, Sep 2, 2011 at 12:59 PM, Dave Young wrote:
    > > > > On Fri, Sep 2, 2011 at 3:10 AM, Sitsofe Wheeler wrote:
    > > > >> On Thu, Sep 01, 2011 at 05:02:51PM +0800, Dave Young wrote:
    > > > >>> On Tue, Aug 30, 2011 at 4:48 AM, Sitsofe Wheeler wrote:
    > > > >>> > I managed to produce an oops in 3.1.0-rc3-00270-g7a54f5e by
    > > > >>> > unplugging a
    > > > >>>
    > > > >>> > USB webcam. See below:
    > > > >>> Could you try the attached patch?
    > > > >>
    > > > >> This patch fixed the oops but extending the sequence (enable camera,
    > > > >> start cheese, disable camera, watch cheese pause, enable camera, quit
    > > > >> cheese, start cheese) causes the following "poison overwritten"
    > > > >> warning
    > > > >
    > > > >> to appear:
    > > > > It seems another bug, I can reproduce this as well.
    > > > >
    > > > > uvc_device is freed in uvc_delete,
    > > > >
    > > > > struct v4l2_device vdev is the member of struct uvc_device, so vdev is
    > > > > also freed. Later v4l2_device operations on vdev will overwrite the
    > > > > poison memory area.
    > > >
    > > > Please try attached patch on top of previous one, in this patch I
    > > > move v4l2_device_put after vdev->release in function
    > > > v4l2_device_release
    > > >
    > > > Not sure if this is a right fix, comments?
    >
    > (inlining the patch's contents)
    >
    > > > diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-
    > > > dev.c
    > > > index 98cee19..541dba3 100644
    > > > --- a/drivers/media/video/v4l2-dev.c
    > > > +++ b/drivers/media/video/v4l2-dev.c
    > > > @@ -172,13 +172,14 @@ static void v4l2_device_release(struct device *cd)
    > > > media_device_unregister_entity(&vdev->entity);
    > > > #endif
    > > >
    > > > + /* Decrease v4l2_device refcount */
    > > > + if (vdev->v4l2_dev)
    > > > + v4l2_device_put(vdev->v4l2_dev);
    > > > +
    > > > /* Release video_device and perform other
    > > > cleanups as needed. */
    > > > vdev->release(vdev);
    > > >
    > > > - /* Decrease v4l2_device refcount */
    > > > - if (vdev->v4l2_dev)
    > > > - v4l2_device_put(vdev->v4l2_dev);
    > > > }
    > > >
    > > > static struct class video_class = {
    >
    > v4l2_device_put() got introduced in commit
    > bedf8bcf6b4f90a6e31add3721a2e71877289381 ("v4l2-device: add kref and a release
    > function"). If I understand its purpose correctly, drivers that use a
    > v4l2_device instance should use the v4l2_device release callback to release
    > device structures instead of counting video_device release callbacks manually.
    > In that case I think the v4l2-dev.c code is correct, and all drivers that use
    > v4l2_device should be fixed.
    >
    > The above patch fixes the problem in a central location, but seems to defeat
    > the original purpose of v4l2_device_get/put().
    >
    > Hans, could you please comment on that ?

    The original order is correct, but what I missed is that for drivers that release
    (free) everything in the videodev release callback the v4l2_device struct is
    also freed and v4l2_device_put will fail.

    To fix this, add this code just before the vdev->release call:

    /* Do not call v4l2_device_put if there is no release callback set. */
    if (v4l2_dev->release == NULL)
    v4l2_dev = NULL;

    If there is no release callback, then the refcounting is pointless anyway.

    This should work.

    Regards,

    Hans

    >
    > > >
    > > > >> [ 191.240695] uvcvideo: Found UVC 1.00 device CNF7129 (04f2:b071)
    > > > >> [ 191.277965] input: CNF7129 as
    > > > >> /devices/pci0000:00/0000:00:1d.7/usb1/1-8/1-8:1.0/input/input9 [
    > > > >> 220.287366]
    > > > >> =====================================================================
    > > > >> ======== [ 220.287379] BUG kmalloc-512: Poison overwritten
    > > > >> [ 220.287384]
    > > > >> ---------------------------------------------------------------------
    > > > >> -------- [ 220.287387]
    > > > >> [ 220.287394] INFO: 0xec90f150-0xec90f150. First byte 0x6a instead of
    > > > >> 0x6b [ 220.287410] INFO: Allocated in uvc_probe+0x54/0xd50
    > > > >> age=210617 cpu=0 pid=16 [ 220.287421] T.974+0x29d/0x5e0
    > > > >> [ 220.287427] kmem_cache_alloc+0x167/0x180
    > > > >> [ 220.287433] uvc_probe+0x54/0xd50
    > > > >> [ 220.287441] usb_probe_interface+0xd5/0x1d0
    > > > >> [ 220.287448] driver_probe_device+0x80/0x1a0
    > > > >> [ 220.287455] __device_attach+0x41/0x50
    > > > >> [ 220.287460] bus_for_each_drv+0x53/0x80
    > > > >> [ 220.287466] device_attach+0x89/0xa0
    > > > >> [ 220.287472] bus_probe_device+0x25/0x40
    > > > >> [ 220.287478] device_add+0x5a9/0x660
    > > > >> [ 220.287484] usb_set_configuration+0x562/0x670
    > > > >> [ 220.287491] generic_probe+0x36/0x90
    > > > >> [ 220.287497] usb_probe_device+0x24/0x50
    > > > >> [ 220.287503] driver_probe_device+0x80/0x1a0
    > > > >> [ 220.287509] __device_attach+0x41/0x50
    > > > >> [ 220.287515] bus_for_each_drv+0x53/0x80
    > > > >> [ 220.287522] INFO: Freed in uvc_delete+0xfe/0x110 age=22 cpu=0
    > > > >> pid=1645 [ 220.287530] __slab_free+0x1f8/0x300
    > > > >> [ 220.287536] kfree+0x100/0x140
    > > > >> [ 220.287541] uvc_delete+0xfe/0x110
    > > > >> [ 220.287547] uvc_release+0x25/0x30
    > > > >> [ 220.287555] v4l2_device_release+0x9d/0xc0
    > > > >> [ 220.287560] device_release+0x19/0x90
    > > > >> [ 220.287567] kobject_release+0x3c/0x90
    > > > >> [ 220.287573] kref_put+0x2c/0x60
    > > > >> [ 220.287578] kobject_put+0x1d/0x50
    > > > >> [ 220.287587] put_device+0xf/0x20
    > > > >> [ 220.287593] v4l2_release+0x56/0x60
    > > > >> [ 220.287599] fput+0xcc/0x220
    > > > >> [ 220.287605] filp_close+0x44/0x70
    > > > >> [ 220.287613] put_files_struct+0x158/0x180
    > > > >> [ 220.287619] exit_files+0x40/0x50
    >
    > [snip]
    >
    >


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