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[209.85.219.50]) by smtp.gmail.com with ESMTPSA id jf8-20020a0562142a4800b006942dcac56asm4207890qvb.103.2024.03.25.09.37.59 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 Mar 2024 09:37:59 -0700 (PDT) Received: by mail-qv1-f50.google.com with SMTP id 6a1803df08f44-696719f8dfcso19633976d6.0 for ; Mon, 25 Mar 2024 09:37:59 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCWPBhk9w4H8VEgWDlfQZ8tSMvlpcI30+TwXA0LMnuB8T7ahjS+i+oLMUFcD1Holfkf+gTxTHP9D5boeoTuBOPgqgyte9O7OUbzGORG5 X-Received: by 2002:a05:6214:1d0e:b0:696:33e9:e0 with SMTP id e14-20020a0562141d0e00b0069633e900e0mr9952116qvd.35.1711384679037; Mon, 25 Mar 2024 09:37:59 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20231122-guenter-mini-v5-0-15d8cd8ed74f@chromium.org> <20231122-guenter-mini-v5-1-15d8cd8ed74f@chromium.org> In-Reply-To: From: Ricardo Ribalda Date: Mon, 25 Mar 2024 17:37:43 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 1/3] media: uvcvideo: Lock video streams and queues while unregistering To: Hans Verkuil Cc: Mauro Carvalho Chehab , Guenter Roeck , Tomasz Figa , Laurent Pinchart , Alan Stern , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Sean Paul , Sakari Ailus , Sergey Senozhatsky Content-Type: text/plain; charset="UTF-8" Hi Hans On Thu, 21 Mar 2024 at 16:47, Hans Verkuil wrote: > > Hi Ricardo, > > On 22/11/2023 12:45 pm, Ricardo Ribalda wrote: > > From: Guenter Roeck > > > > The call to uvc_disconnect() is not protected by any mutex. > > This means it can and will be called while other accesses to the video > > device are in progress. This can cause all kinds of race conditions, > > including crashes such as the following. > > > > 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 > > > > usb_set_interface() should not be called after the USB device has been > > unregistered. However, in the above case the disconnect happened after > > v4l2_ioctl() was called, but before the call to usb_ifnum_to_if(). > > > > Acquire various mutexes in uvc_unregister_video() to fix the majority > > (maybe all) of the observed race conditions. > > > > The uvc_device lock prevents races against suspend and resume calls > > and the poll function. > > > > The uvc_streaming lock prevents races against stream related functions; > > for the most part, those are ioctls. This lock also requires other > > functions using this lock to check if a video device is still registered > > after acquiring it. For example, it was observed that the video device > > was already unregistered by the time the stream lock was acquired in > > uvc_ioctl_streamon(). > > > > The uvc_queue lock prevents races against queue functions, Most of > > those are already protected by the uvc_streaming lock, but some > > are called directly. This is done as added protection; an actual race > > was not (yet) observed. > > > > Cc: Laurent Pinchart > > Cc: Alan Stern > > Cc: Hans Verkuil > > Reviewed-by: Tomasz Figa > > Reviewed-by: Sean Paul > > Signed-off-by: Guenter Roeck > > Reviewed-by: Sergey Senozhatsky > > Signed-off-by: Ricardo Ribalda > > --- > > drivers/media/usb/uvc/uvc_driver.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > > index 08fcd2ffa727..ded2cb6ce14f 100644 > > --- a/drivers/media/usb/uvc/uvc_driver.c > > +++ b/drivers/media/usb/uvc/uvc_driver.c > > @@ -1907,14 +1907,22 @@ static void uvc_unregister_video(struct uvc_device *dev) > > { > > struct uvc_streaming *stream; > > > > + mutex_lock(&dev->lock); > > + > > list_for_each_entry(stream, &dev->streams, list) { > > if (!video_is_registered(&stream->vdev)) > > continue; > > > > + mutex_lock(&stream->mutex); > > + mutex_lock(&stream->queue.mutex); > > + > > video_unregister_device(&stream->vdev); > > video_unregister_device(&stream->meta.vdev); > > > > uvc_debugfs_cleanup_stream(stream); > > + > > + mutex_unlock(&stream->queue.mutex); > > + mutex_unlock(&stream->mutex); > > Part of the problem here is that video_unregister_device does not stop streaming. > > For 'normal' drivers that leave most of the locking to the core framework and > that use the standard vb2_fop_* and vb2_ioctl_* helpers, instead of calling > video_unregister_device, they call vb2_video_unregister_device(). This will > safely unregister the device and stop streaming at the same time. > > Since after the device is unregistered the only file operation that is accepted > is close(), it will be impossible to restart streaming. > > In other words, this guarantees that when the disconnect function exits there > is nothing streaming anymore. I have tested this approach and it seems to work :) I have updated and sent for review, and in the meantime I will continue torturing my device to figure out if we are missing any other race. Thanks! > > This makes it much easier to deal with disconnects, and I think this should > happen here as well. I wonder if this will obsolete patch 3/3 and perhaps > 2/3. > > I don't think taking the queue.mutex is needed, especially if you stop > streaming here. > > Regards, > > Hans > > > } > > > > uvc_status_unregister(dev); > > @@ -1925,6 +1933,7 @@ static void uvc_unregister_video(struct uvc_device *dev) > > if (media_devnode_is_registered(dev->mdev.devnode)) > > media_device_unregister(&dev->mdev); > > #endif > > + mutex_unlock(&dev->lock); > > } > > > > int uvc_register_video_device(struct uvc_device *dev, > > > -- Ricardo Ribalda