On Wed, 29 Oct 2025 at 04:01, Mathieu Poirier <[email protected]> wrote: > > Hi Patrick, > > I started reviewing this patch. Despite the short amount of code, it will > take > me a few days to understand the ramifications of your proposal. > > Thanks, > Mathieu
Thanks, I appreciate you taking the time to look at it. This really should be considered a bug fix. If userspace does something like this: struct epoll_event ev; ev.events = EPOLLOUT; epoll_ctl(epfd, EPOLL_CTL_ADD, rpmsg_fd, &ev); epoll_ctl will return without error, but never generate any events for rpmsg_fd. Patrick > On Wed, Oct 22, 2025 at 02:28:17PM +1100, [email protected] wrote: > > From: Patrick Oppenlander <[email protected]> > > > > Previously, polling an rpmsg endpoint (e.g. /dev/ttyRPMSGx) would > > generate EPOLLIN events but no EPOLLOUT events. > > > > Unfortunately, poll support means that we can no longer disable > > tx-complete interrupts as there is no way to know whether a poller is > > waiting in sendq, so we always need notifications. > > > > Signed-off-by: Patrick Oppenlander <[email protected]> > > --- > > drivers/rpmsg/virtio_rpmsg_bus.c | 101 ++++++++++--------------------- > > 1 file changed, 32 insertions(+), 69 deletions(-) > > > > diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c > > b/drivers/rpmsg/virtio_rpmsg_bus.c > > index 484890b4a6a74..79d983055b4d6 100644 > > --- a/drivers/rpmsg/virtio_rpmsg_bus.c > > +++ b/drivers/rpmsg/virtio_rpmsg_bus.c > > @@ -41,13 +41,12 @@ > > * @buf_size: size of one rx or tx buffer > > * @last_sbuf: index of last tx buffer used > > * @bufs_dma: dma base addr of the buffers > > - * @tx_lock: protects svq, sbufs and sleepers, to allow concurrent senders. > > + * @tx_lock: protects svq and sbufs, to allow concurrent senders. > > * sending a message might require waking up a dozing remote > > * processor, which involves sleeping, hence the mutex. > > * @endpoints: idr of local endpoints, allows fast retrieval > > * @endpoints_lock: lock of the endpoints set > > * @sendq: wait queue of sending contexts waiting for a tx buffers > > - * @sleepers: number of senders that are waiting for a tx buffer > > * > > * This structure stores the rpmsg state of a given virtio remote processor > > * device (there might be several virtio proc devices for each physical > > @@ -65,7 +64,6 @@ struct virtproc_info { > > struct idr endpoints; > > struct mutex endpoints_lock; > > wait_queue_head_t sendq; > > - atomic_t sleepers; > > }; > > > > /* The feature bitmap for virtio rpmsg */ > > @@ -144,6 +142,8 @@ static int virtio_rpmsg_sendto(struct rpmsg_endpoint > > *ept, void *data, int len, > > static int virtio_rpmsg_trysend(struct rpmsg_endpoint *ept, void *data, > > int len); > > static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data, > > int len, u32 dst); > > +static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file > > *filp, > > + poll_table *wait); > > static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept); > > static struct rpmsg_device *__rpmsg_create_channel(struct virtproc_info > > *vrp, > > struct rpmsg_channel_info > > *chinfo); > > @@ -154,6 +154,7 @@ static const struct rpmsg_endpoint_ops > > virtio_endpoint_ops = { > > .sendto = virtio_rpmsg_sendto, > > .trysend = virtio_rpmsg_trysend, > > .trysendto = virtio_rpmsg_trysendto, > > + .poll = virtio_rpmsg_poll, > > .get_mtu = virtio_rpmsg_get_mtu, > > }; > > > > @@ -436,7 +437,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp) > > unsigned int len; > > void *ret; > > > > - /* support multiple concurrent senders */ > > mutex_lock(&vrp->tx_lock); > > > > /* > > @@ -454,62 +454,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp) > > return ret; > > } > > > > -/** > > - * rpmsg_upref_sleepers() - enable "tx-complete" interrupts, if needed > > - * @vrp: virtual remote processor state > > - * > > - * This function is called before a sender is blocked, waiting for > > - * a tx buffer to become available. > > - * > > - * If we already have blocking senders, this function merely increases > > - * the "sleepers" reference count, and exits. > > - * > > - * Otherwise, if this is the first sender to block, we also enable > > - * virtio's tx callbacks, so we'd be immediately notified when a tx > > - * buffer is consumed (we rely on virtio's tx callback in order > > - * to wake up sleeping senders as soon as a tx buffer is used by the > > - * remote processor). > > - */ > > -static void rpmsg_upref_sleepers(struct virtproc_info *vrp) > > -{ > > - /* support multiple concurrent senders */ > > - mutex_lock(&vrp->tx_lock); > > - > > - /* are we the first sleeping context waiting for tx buffers ? */ > > - if (atomic_inc_return(&vrp->sleepers) == 1) > > - /* enable "tx-complete" interrupts before dozing off */ > > - virtqueue_enable_cb(vrp->svq); > > - > > - mutex_unlock(&vrp->tx_lock); > > -} > > - > > -/** > > - * rpmsg_downref_sleepers() - disable "tx-complete" interrupts, if needed > > - * @vrp: virtual remote processor state > > - * > > - * This function is called after a sender, that waited for a tx buffer > > - * to become available, is unblocked. > > - * > > - * If we still have blocking senders, this function merely decreases > > - * the "sleepers" reference count, and exits. > > - * > > - * Otherwise, if there are no more blocking senders, we also disable > > - * virtio's tx callbacks, to avoid the overhead incurred with handling > > - * those (now redundant) interrupts. > > - */ > > -static void rpmsg_downref_sleepers(struct virtproc_info *vrp) > > -{ > > - /* support multiple concurrent senders */ > > - mutex_lock(&vrp->tx_lock); > > - > > - /* are we the last sleeping context waiting for tx buffers ? */ > > - if (atomic_dec_and_test(&vrp->sleepers)) > > - /* disable "tx-complete" interrupts */ > > - virtqueue_disable_cb(vrp->svq); > > - > > - mutex_unlock(&vrp->tx_lock); > > -} > > - > > /** > > * rpmsg_send_offchannel_raw() - send a message across to the remote > > processor > > * @rpdev: the rpmsg channel > > @@ -582,9 +526,6 @@ static int rpmsg_send_offchannel_raw(struct > > rpmsg_device *rpdev, > > > > /* no free buffer ? wait for one (but bail after 15 seconds) */ > > while (!msg) { > > - /* enable "tx-complete" interrupts, if not already enabled */ > > - rpmsg_upref_sleepers(vrp); > > - > > /* > > * sleep until a free buffer is available or 15 secs elapse. > > * the timeout period is not configurable because there's > > @@ -595,9 +536,6 @@ static int rpmsg_send_offchannel_raw(struct > > rpmsg_device *rpdev, > > (msg = get_a_tx_buf(vrp)), > > msecs_to_jiffies(15000)); > > > > - /* disable "tx-complete" interrupts if we're the last sleeper > > */ > > - rpmsg_downref_sleepers(vrp); > > - > > /* timeout ? */ > > if (!err) { > > dev_err(dev, "timeout waiting for a tx buffer\n"); > > @@ -676,6 +614,34 @@ static int virtio_rpmsg_trysendto(struct > > rpmsg_endpoint *ept, void *data, > > return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false); > > } > > > > +static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file > > *filp, > > + poll_table *wait) > > +{ > > + struct rpmsg_device *rpdev = ept->rpdev; > > + struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev); > > + struct virtproc_info *vrp = vch->vrp; > > + __poll_t mask = 0; > > + > > + poll_wait(filp, &vrp->sendq, wait); > > + > > + /* support multiple concurrent senders */ > > + mutex_lock(&vrp->tx_lock); > > + > > + /* > > + * check for a free buffer, either: > > + * - we haven't used all of the available transmit buffers (half of > > the > > + * allocated buffers are used for transmit, hence num_bufs / 2), or, > > + * - we ask the virtqueue if there's a buffer available > > + */ > > + if (vrp->last_sbuf < vrp->num_bufs / 2 || > > + !virtqueue_enable_cb(vrp->svq)) > > + mask |= EPOLLOUT; > > + > > + mutex_unlock(&vrp->tx_lock); > > + > > + return mask; > > +} > > + > > static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept) > > { > > struct rpmsg_device *rpdev = ept->rpdev; > > @@ -922,9 +888,6 @@ static int rpmsg_probe(struct virtio_device *vdev) > > WARN_ON(err); /* sanity check; this can't really happen */ > > } > > > > - /* suppress "tx-complete" interrupts */ > > - virtqueue_disable_cb(vrp->svq); > > - > > vdev->priv = vrp; > > > > rpdev_ctrl = rpmsg_virtio_add_ctrl_dev(vdev); > > -- > > 2.51.1.dirty > >
