On 10/5/23 15:05, Michael Grzeschik wrote: > Hi Avichal, > > On Thu, Oct 05, 2023 at 11:30:32AM -0700, Avichal Rakesh wrote: >> On 10/5/23 03:14, Michael Grzeschik wrote: >>> On Thu, Oct 05, 2023 at 11:23:27AM +0300, Laurent Pinchart wrote: >>>> On Tue, Oct 03, 2023 at 01:09:06PM +0200, Michael Grzeschik wrote: >>>>> On Sat, Sep 30, 2023 at 11:48:18AM -0700, Avichal Rakesh wrote: >>>>> > We have been seeing two main stability issues that uvc gadget driver >>>>> > runs into when stopping streams: >>>>> > 1. Attempting to queue usb_requests to a disabled usb_ep >>>>> > 2. use-after-free issue for inflight usb_requests >>>>> > >>>>> > The three patches below fix the two issues above. Patch 1/3 fixes the >>>>> > first issue, and Patch 2/3 and 3/3 fix the second issue. >>>>> > >>>>> > Avichal Rakesh (3): >>>>> > usb: gadget: uvc: prevent use of disabled endpoint >>>>> > usb: gadget: uvc: Allocate uvc_requests one at a time >>>>> > usb: gadget: uvc: Fix use-after-free for inflight usb_requests >>>>> > >>>>> > drivers/usb/gadget/function/f_uvc.c | 11 +- >>>>> > drivers/usb/gadget/function/f_uvc.h | 2 +- >>>>> > drivers/usb/gadget/function/uvc.h | 6 +- >>>>> > drivers/usb/gadget/function/uvc_v4l2.c | 21 ++- >>>>> > drivers/usb/gadget/function/uvc_video.c | 189 +++++++++++++++++------- >>>>> > 5 files changed, 164 insertions(+), 65 deletions(-) >>>>> >>>>> These patches are not applying on gregkh/usb-testing since >>>>> Greg did take my patches first. I have already rebased them. >>>> >>>> I think they got merged too soon :-( We could fix things on top, but >>>> there's very little time to do so for v6.7. >>> >>> Agreed. I was jumping from one workaround to another one, since this >>> is not easy to fix in a proper way. And still after this long discussion >>> with Avichal I don't think we are there yet. >>> >>> >>> So far the first two patches from Avichal look legit. But the overall >>> Use-After-Free fix is yet to be done properly. >>> >>> The "abondoned" method he suggested is really bad to follow and will >>> add too much complexity and will be hard to debug. >>> >>> IMHO it should be possible to introduce two cleanup pathes. >>> >>> One path would be in the uvc_cleanup_requests that will cleanup the >>> requests that are actually not used in the controller and are registered >>> in the req_free list. >>> >>> The second path would be the complete functions that are being run >>> from the controller and will ensure that the cleanup will really free >>> the requests from the controller after they were consumed. >>> >>> What do you think? >> >> I am not sure I follow. Patch 3/3 does exactly what you say here. > > Yes, it was just to summ up what the latest state of the idea was, > so Laurent does not read the whole thread in detail. Sorry for not > being clear enough about that. Whoops! Sorry about the misunderstanding! > >> There are two cleanup paths: >> 1. uvcg_video_disable cleans up only the requests in req_free, and >> 2. complete handler cleans up the in-flight requests. >> >> The "abandoned" flag is simply to let the completion handler know >> which requests to clean up and which ones to re-queue back to >> the gadget driver. > > What I don't get is, why in the case of shutdown there needs to > be something re-queued back to the gadget driver. There should not > need to be any sort of barrier flag for the requests. Just the > complete handler running past a barrier where it knows that the > whole device is stopped. So every call on complete should then clean > that exact request it is touching currently. > > I don't know where the extra complexity comes from. A lot of this complexity comes from assuming a back to back STREAMOFF -> STREAMON sequence is possible where the gadget driver doesn't have the time to clean up all in-flight usb_requests. However, looking through the usb gadget APIs again, and it looks like usb_ep_disable enforces that all requests will be sent back to the gadget driver before it returns. So you're right: With Patch 1/3 in place, I think we can just guard on uvc->state alone, because control requests are blocked until usb_ep_disable is finished anyway. I'll upload v4 with the "is_abandoned" flag removed and the checks simplified once I've verified the fix locally. That should also remove any bookkeeping issues that may have triggered the stack below. Regards, Avi. > >> The other "complications" are around making sure we can trust >> the values in an inherently racey situation. The reasoning >> can admittedly be difficult to follow at a glance, which incidentally >> is why I went with a simple to prove timed wait in the past >> (https://lore.kernel.org/20230912041910.726442-3-arakesh@xxxxxxxxxx). >> >> I am not suggesting we go back to a timed wait, but please do look >> at the patch and let me know which parts don't make sense, or are >> difficult to understand. We can add more documentation about our >> assumptions there, or if you have a way to do this that you >> think is simpler to reason about, then please let me know and I'll >> be more than happy to use that! > > I really try to spin my head around the idea of the is_abondoned flag > you are using. Unfortunatly for now I am out to debug the issues I see > with your series. > > So I did try these patches you send. Yes the deadlock error is gone with > v3. But the linked list is still running into cases where > dwc3_gadget_giveback(complete) is touching requests that are already > freed. > > [ 61.408715] ------------[ cut here ]------------ > [ 61.413897] kernel BUG at lib/list_debug.c:56! > ... > [ 61.590762] Call trace: > [ 61.596890] __list_del_entry_valid+0xb8/0xe8 > [ 61.603408] dwc3_gadget_giveback+0x3c/0x1b0 > [ 61.607594] dwc3_remove_requests.part.0+0xcc/0x100 > [ 61.612948] __dwc3_gadget_ep_disable+0xbc/0x1b8 > [ 61.621019] dwc3_gadget_ep_disable+0x48/0x100 > [ 61.627925] usb_ep_disable+0x3c/0x138 > [ 61.638230] uvc_function_setup_continue+0x3c/0x60 > [ 61.645040] uvc_v4l2_streamoff+0x5c/0x80 > [ 61.659812] v4l_streamoff+0x40/0x60 > [ 61.668950] __video_do_ioctl+0x344/0x420 > [ 61.679548] video_usercopy+0x1d0/0x788 > [ 61.685677] video_ioctl2+0x40/0x70 > [ 61.697439] v4l2_ioctl+0x68/0xa0 > [ 61.709200] __arm64_sys_ioctl+0x304/0xda0 > [ 61.720768] invoke_syscall.constprop.0+0x70/0x130 >
