hello, I sent a email about 'can't wake problem' 4 days ago. Is this problem related with mine? > epoll and vb2_poll: can't wake_up > Sun, Dec 30, 2018, 6:17 PM (4 days ago) > to linux-kernel > Hello, I encountered a "can't wake_up" problem when use camera on imx6. > > if delay some time after 'streamon' the /dev/video0, then add fd > through epoll_ctl, then the process can't be waken_up after some time. > > I checked both the epoll / vb2_poll(videobuf2_core.c) code. > > epoll will pass 'poll_table' structure to vb2_poll, but it only > contain valid function pointer when inserting fd. > > in vb2_poll, if found new data in done list, it will not call 'poll_wait'. > after that, every call to vb2_poll will not contain valid poll_table, > which will result in all calling to poll_wait will not work. > > so if app can process frames quickly, and found frame data when > inserting fd (i.e. poll_wait will not be called or not contain valid > function pointer), it will not found valid frame in 'vb2_poll' finally > at some time, then call 'poll_wait' to expect be waken up at following > vb2_buffer_done, but no good luck. > > I also checked the 'videobuf-core.c', there is no this problem. > > of course, both epoll and vb2_poll are right by itself side, but the > result is we can't get new frames. > > I think by epoll's implementation, the user should always call poll_wait. > > and it's better to split the two actions: 'wait' and 'poll' both for > epoll framework and all epoll users, for example, v4l2. > > am I right? On Thu, Jan 3, 2019 at 4:17 AM Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2018-11-08 at 14:03 +0200, Sakari Ailus wrote: > > [ upstream commit 92539d3eda2c090b382699bbb896d4b54e9bdece ] > > > > Patch ad608fbcf166 changed how events were subscribed to address an issue > > elsewhere. As a side effect of that change, the "add" callback was called > > before the event subscription was added to the list of subscribed events, > > causing the first event queued by the add callback (and possibly other > > events arriving soon afterwards) to be lost. > > > > Fix this by adding the subscription to the list before calling the "add" > > callback, and clean up afterwards if that fails. > [...] > > I've queued this up for the next update, thanks. > > Ben. > > -- > Ben Hutchings > Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer > >
