From 5a081caa0414b9bbb82c17ffab9d6fe66edbb72f Mon Sep 17 00:00:00 2001 From: Ohad Ben-Cohen Date: Wed, 6 Jun 2012 10:09:25 +0300 Subject: rpmsg: avoid premature deallocation of endpoints When an inbound message arrives, the rpmsg core looks up its associated endpoint and invokes the registered callback. If a message arrives while its endpoint is being removed (because the rpmsg driver was removed, or a recovery of a remote processor has kicked in) we must ensure atomicity, i.e.: - Either the ept is removed before it is found or - The ept is found but will not be freed until the callback returns This is achieved by maintaining a per-ept reference count, which, when drops to zero, will trigger deallocation of the ept. With this in hand, it is now forbidden to directly deallocate epts once they have been added to the endpoints idr. Cc: stable Reported-by: Fernando Guzman Lugo Signed-off-by: Ohad Ben-Cohen --- drivers/rpmsg/virtio_rpmsg_bus.c | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) (limited to 'drivers') diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c index 75506ec2840..9623327ba50 100644 --- a/drivers/rpmsg/virtio_rpmsg_bus.c +++ b/drivers/rpmsg/virtio_rpmsg_bus.c @@ -188,6 +188,26 @@ static int rpmsg_uevent(struct device *dev, struct kobj_uevent_env *env) rpdev->id.name); } +/** + * __ept_release() - deallocate an rpmsg endpoint + * @kref: the ept's reference count + * + * This function deallocates an ept, and is invoked when its @kref refcount + * drops to zero. + * + * Never invoke this function directly! + */ +static void __ept_release(struct kref *kref) +{ + struct rpmsg_endpoint *ept = container_of(kref, struct rpmsg_endpoint, + refcount); + /* + * At this point no one holds a reference to ept anymore, + * so we can directly free it + */ + kfree(ept); +} + /* for more info, see below documentation of rpmsg_create_ept() */ static struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp, struct rpmsg_channel *rpdev, rpmsg_rx_cb_t cb, @@ -206,6 +226,8 @@ static struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp, return NULL; } + kref_init(&ept->refcount); + ept->rpdev = rpdev; ept->cb = cb; ept->priv = priv; @@ -238,7 +260,7 @@ rem_idr: idr_remove(&vrp->endpoints, request); free_ept: mutex_unlock(&vrp->endpoints_lock); - kfree(ept); + kref_put(&ept->refcount, __ept_release); return NULL; } @@ -306,7 +328,7 @@ __rpmsg_destroy_ept(struct virtproc_info *vrp, struct rpmsg_endpoint *ept) idr_remove(&vrp->endpoints, ept->addr); mutex_unlock(&vrp->endpoints_lock); - kfree(ept); + kref_put(&ept->refcount, __ept_release); } /** @@ -790,7 +812,13 @@ static void rpmsg_recv_done(struct virtqueue *rvq) /* use the dst addr to fetch the callback of the appropriate user */ mutex_lock(&vrp->endpoints_lock); + ept = idr_find(&vrp->endpoints, msg->dst); + + /* let's make sure no one deallocates ept while we use it */ + if (ept) + kref_get(&ept->refcount); + mutex_unlock(&vrp->endpoints_lock); if (ept && ept->cb) @@ -798,6 +826,10 @@ static void rpmsg_recv_done(struct virtqueue *rvq) else dev_warn(dev, "msg received with no recepient\n"); + /* farewell, ept, we don't need you anymore */ + if (ept) + kref_put(&ept->refcount, __ept_release); + /* publish the real size of the buffer */ sg_init_one(&sg, msg, RPMSG_BUF_SIZE); -- cgit v1.2.3 From 15fd943af50dbc5f7f4de33835795c72595f7bf4 Mon Sep 17 00:00:00 2001 From: Ohad Ben-Cohen Date: Thu, 7 Jun 2012 15:39:35 +0300 Subject: rpmsg: make sure inflight messages don't invoke just-removed callbacks When inbound messages arrive, rpmsg core looks up their associated endpoint (by destination address) and then invokes their callback. We've made sure that endpoints will never be de-allocated after they were found by rpmsg core, but we also need to protect against the (rare) scenario where the rpmsg driver was just removed, and its callback function isn't available anymore. This is achieved by introducing a callback mutex, which must be taken before the callback is invoked, and, obviously, before it is removed. Cc: stable Reported-by: Fernando Guzman Lugo Signed-off-by: Ohad Ben-Cohen --- drivers/rpmsg/virtio_rpmsg_bus.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) (limited to 'drivers') diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c index 9623327ba50..39d3aa41add 100644 --- a/drivers/rpmsg/virtio_rpmsg_bus.c +++ b/drivers/rpmsg/virtio_rpmsg_bus.c @@ -227,6 +227,7 @@ static struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp, } kref_init(&ept->refcount); + mutex_init(&ept->cb_lock); ept->rpdev = rpdev; ept->cb = cb; @@ -324,10 +325,16 @@ EXPORT_SYMBOL(rpmsg_create_ept); static void __rpmsg_destroy_ept(struct virtproc_info *vrp, struct rpmsg_endpoint *ept) { + /* make sure new inbound messages can't find this ept anymore */ mutex_lock(&vrp->endpoints_lock); idr_remove(&vrp->endpoints, ept->addr); mutex_unlock(&vrp->endpoints_lock); + /* make sure in-flight inbound messages won't invoke cb anymore */ + mutex_lock(&ept->cb_lock); + ept->cb = NULL; + mutex_unlock(&ept->cb_lock); + kref_put(&ept->refcount, __ept_release); } @@ -821,14 +828,20 @@ static void rpmsg_recv_done(struct virtqueue *rvq) mutex_unlock(&vrp->endpoints_lock); - if (ept && ept->cb) - ept->cb(ept->rpdev, msg->data, msg->len, ept->priv, msg->src); - else - dev_warn(dev, "msg received with no recepient\n"); + if (ept) { + /* make sure ept->cb doesn't go away while we use it */ + mutex_lock(&ept->cb_lock); - /* farewell, ept, we don't need you anymore */ - if (ept) + if (ept->cb) + ept->cb(ept->rpdev, msg->data, msg->len, ept->priv, + msg->src); + + mutex_unlock(&ept->cb_lock); + + /* farewell, ept, we don't need you anymore */ kref_put(&ept->refcount, __ept_release); + } else + dev_warn(dev, "msg received with no recepient\n"); /* publish the real size of the buffer */ sg_init_one(&sg, msg, RPMSG_BUF_SIZE); -- cgit v1.2.3