Hi Guenter, On Wed, Sep 16, 2020 at 07:25:42PM -0700, Guenter Roeck wrote: > Something seems to have gone wrong with v3 of this patch series. > I am sure I sent it out, but I don't find it anywhere. > Resending. Sorry for any duplicates. I haven't checked the mailing list, but I've found it in my inbox :-) I'm not forgetting about you, just been fairly busy recently. I still plan to try and provide an alternative implementation in the V4L2 core (in a form that I think should even be moved to the cdev core) that would fix this for all drivers. By the way, as you managed to get hold of non-UVC webcams, one thing you could try in your tests to make the drivers misbehave is to block on a DQBUF call, and unplug the device at that time. When blocking, DQBUF releases the driver lock (through the vb2ops .wait_prepare() and .wait_finis() operations for drivers based on vb2), so this may allow unregistration to proceed without waiting for userspace calls to complete. > The uvcvideo code has no lock protection against USB disconnects > while video operations are ongoing. This has resulted in random > error reports, typically pointing to a crash in usb_ifnum_to_if(), > called from usb_hcd_alloc_bandwidth(). A typical traceback is as > follows. > > usb 1-4: USB disconnect, device number 3 > BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 > PGD 0 P4D 0 > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 0 PID: 5633 Comm: V4L2CaptureThre Not tainted 4.19.113-08536-g5d29ca36db06 #1 > Hardware name: GOOGLE Edgar, BIOS Google_Edgar.7287.167.156 03/25/2019 > RIP: 0010:usb_ifnum_to_if+0x29/0x40 > Code: <...> > RSP: 0018:ffffa46f42a47a80 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff904a396c9000 > RDX: ffff904a39641320 RSI: 0000000000000001 RDI: 0000000000000000 > RBP: ffffa46f42a47a80 R08: 0000000000000002 R09: 0000000000000000 > R10: 0000000000009975 R11: 0000000000000009 R12: 0000000000000000 > R13: ffff904a396b3800 R14: ffff904a39e88000 R15: 0000000000000000 > FS: 00007f396448e700(0000) GS:ffff904a3ba00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000000 CR3: 000000016cb46000 CR4: 00000000001006f0 > Call Trace: > usb_hcd_alloc_bandwidth+0x1ee/0x30f > usb_set_interface+0x1a3/0x2b7 > uvc_video_start_transfer+0x29b/0x4b8 [uvcvideo] > uvc_video_start_streaming+0x91/0xdd [uvcvideo] > uvc_start_streaming+0x28/0x5d [uvcvideo] > vb2_start_streaming+0x61/0x143 [videobuf2_common] > vb2_core_streamon+0xf7/0x10f [videobuf2_common] > uvc_queue_streamon+0x2e/0x41 [uvcvideo] > uvc_ioctl_streamon+0x42/0x5c [uvcvideo] > __video_do_ioctl+0x33d/0x42a > video_usercopy+0x34e/0x5ff > ? video_ioctl2+0x16/0x16 > v4l2_ioctl+0x46/0x53 > do_vfs_ioctl+0x50a/0x76f > ksys_ioctl+0x58/0x83 > __x64_sys_ioctl+0x1a/0x1e > do_syscall_64+0x54/0xde > > While there are not many references to this problem on mailing lists, it is > reported on a regular basis on various Chromebooks (roughly 300 reports > per month). The problem is relatively easy to reproduce by adding msleep() > calls into the code. > > I tried to reproduce the problem with non-uvcvideo webcams, but was > unsuccessful. I was unable to get Philips (pwc) webcams to work. gspca > based webcams don't experience the problem, or at least I was unable to > reproduce it (The gspa driver does not trigger sending USB messages in the > open function, and otherwise uses the locking mechanism provided by the > v4l2/vb2 core). > > I don't presume to claim that I found every issue, but this patch series > should fix at least the major problems. > > The patch series was tested exensively on a Chromebook running chromeos-4.19 > and on a Linux system running a v5.8.y based kernel. > > v3: > - In patch 5/5, add missing calls to usb_autopm_put_interface() and kfree() > to failure code path > > v2: > - Added details about problem frequency and testing with non-uvc webcams > to summary > - In patch 4/5, return EPOLLERR instead of -ENODEV on poll errors > - Fix description in patch 5/5 > > ---------------------------------------------------------------- > Guenter Roeck (5): > media: uvcvideo: Cancel async worker earlier > media: uvcvideo: Lock video streams and queues while unregistering > media: uvcvideo: Release stream queue when unregistering video device > media: uvcvideo: Protect uvc queue file operations against disconnect > media: uvcvideo: Abort uvc_v4l2_open if video device is unregistered > > drivers/media/usb/uvc/uvc_ctrl.c | 11 ++++++---- > drivers/media/usb/uvc/uvc_driver.c | 12 ++++++++++ > drivers/media/usb/uvc/uvc_queue.c | 32 +++++++++++++++++++++++++-- > drivers/media/usb/uvc/uvc_v4l2.c | 45 ++++++++++++++++++++++++++++++++++++-- > drivers/media/usb/uvc/uvcvideo.h | 1 + > 5 files changed, 93 insertions(+), 8 deletions(-) -- Regards, Laurent Pinchart
