From: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> As was reported by Yi Qingliang (http://lkml.iu.edu/hypermail/linux/kernel/1812.3/02144.html) the epoll support in v4l2 is broken. After researching this some more it turns out that we never really understood when poll_wait() should be called, and that in fact it is broken in quite a few places in our media tree, and not just v4l2. The select() call is fairly simplistic: it calls the poll fop first, then waits for an event if the poll fop returned 0. The epoll() call is more complicated: epoll_ctl(EPOLL_CTL_ADD) will call the poll fop which calls poll_wait in turn. But epoll_wait() just waits for events to arrive on the registered waitqueues, and does not call the poll fop until it is woken up. So not calling poll_wait() in the poll fop will cause epoll_wait() to wait forever (or until the timeout is reached). This patch series just calls poll_wait() regardless of whether there is an event pending. It does this for all the various frameworks that did this wrong. Note that there is also an extra mem2mem patch that adds a check for q->error, which I noticed was missing. I have not tested the videobuf and esp. the dvb-core changes. They look sane, but it doesn't hurt to give those extra attention. There are also older drivers that call poll_wait themselves. While I have some patches for those (look in https://git.linuxtv.org/hverkuil/media_tree.git/log/?h=poll), they need more review. I prefer to do the core frameworks first. Several of the patches in this series should probably be CC-ed to stable. I'll take a look at that once this RFC series gets the green light. Regards, Hans Hans Verkuil (8): cec: fix epoll() by calling poll_wait first media-request: fix epoll() by calling poll_wait first vb2: fix epoll() by calling poll_wait first v4l2-ctrls.c: fix epoll() by calling poll_wait first v4l2-mem2mem: fix epoll() by calling poll_wait first v4l2-mem2mem: add q->error check to v4l2_m2m_poll() videobuf: fix epoll() by calling poll_wait first dvb-core: fix epoll() by calling poll_wait first drivers/media/cec/cec-api.c | 2 +- .../media/common/videobuf2/videobuf2-core.c | 4 +-- .../media/common/videobuf2/videobuf2-v4l2.c | 4 +-- drivers/media/dvb-core/dmxdev.c | 8 +++--- drivers/media/dvb-core/dvb_ca_en50221.c | 5 ++-- drivers/media/media-request.c | 3 +-- drivers/media/v4l2-core/v4l2-ctrls.c | 2 +- drivers/media/v4l2-core/v4l2-mem2mem.c | 25 ++++++++----------- drivers/media/v4l2-core/videobuf-core.c | 6 ++--- 9 files changed, 26 insertions(+), 33 deletions(-) -- 2.20.1
