Hi Laurent, On 9/17/20 5:47 AM, Laurent Pinchart wrote: > 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. > Thanks for letting me know. As it turns out, this problem is responsible for about 2% of all Chromebook crashes, so I'll probably not wait for the series to be accepted upstream but apply it as-is to the various ChromeOS kernel branches. > 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. > Good idea. I'll give it a try. Thanks, Guenter >> 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(-) >
