On Mon, 2019-01-14 at 14:38 +0100, Paul Kocialkowski wrote: > Introduce a new optional job_done operation, which allows calling back > to the driver when a job is done. Since the job might be completed > from interrupt context where some operations are not available, having > a callback from non-atomic context allows performing these operations > upon completion of a job. This is particularly useful for releasing > access to a reference buffer, which cannot be done in atomic context. > I'm not exactly sure it makes a lot of sense to review this patch, since the approach could change. However, let me point out a few fundamental issues here. > Use the already existing v4l2_m2m_device_run_work work queue for that > and clear the M2M device current context after calling job_done in the > worker thread, so that the private data can be passed to the operation. > > Delaying the current context clearing should not be a problem since the > next call to v4l2_m2m_try_run happens right after that. > Careful here. It's misleading to think an event will happen "right after". I'd say it's either synchronously, or asynchronously. It's quite the opposite I'd say, the clearing will happen "who-knows-when the scheduler picks the thread to run" :-) Before this patch the curr_ctx was cleared in v4l2_m2m_job_finish, atomically with the ctx job flags clearing and before waking up threads waiting in v4l2_m2m_cancel_job. You are now changing this, by clearing curr_ctx in a worker. It's perfectly possible that v4l2_m2m_try_schedule will run before the worker, trying to run with the old context, which apparently would be safely refused. > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> > --- > drivers/media/v4l2-core/v4l2-mem2mem.c | 8 ++++++-- > include/media/v4l2-mem2mem.h | 4 ++++ > 2 files changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c > index 631f4e2aa942..d5bccb0192f9 100644 > --- a/drivers/media/v4l2-core/v4l2-mem2mem.c > +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c > @@ -376,6 +376,11 @@ static void v4l2_m2m_device_run_work(struct work_struct *work) > struct v4l2_m2m_dev *m2m_dev = > container_of(work, struct v4l2_m2m_dev, job_work); > > + if (m2m_dev->m2m_ops->job_done && m2m_dev->curr_ctx) > + m2m_dev->m2m_ops->job_done(m2m_dev->curr_ctx->priv); > + > + m2m_dev->curr_ctx = NULL; > + I don't think you can access this without taking the job spinlock. > v4l2_m2m_try_run(m2m_dev); > } > Aside from this, it seems we might need this hook sooner or later. Thanks, Eze
