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 <stable@vger.kernel.org>
Reported-by: Fernando Guzman Lugo <fernando.lugo@ti.com>
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
index a8e50e44203..195f373590b 100644
--- a/include/linux/rpmsg.h
+++ b/include/linux/rpmsg.h
@@ -38,6 +38,7 @@
 #include <linux/types.h>
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
+#include <linux/kref.h>
 
 /* The feature bitmap for virtio rpmsg */
 #define VIRTIO_RPMSG_F_NS	0 /* RP supports name service notifications */
@@ -120,6 +121,7 @@ typedef void (*rpmsg_rx_cb_t)(struct rpmsg_channel *, void *, int, void *, u32);
 /**
  * struct rpmsg_endpoint - binds a local rpmsg address to its user
  * @rpdev: rpmsg channel device
+ * @refcount: when this drops to zero, the ept is deallocated
  * @cb: rx callback handler
  * @addr: local rpmsg address
  * @priv: private data for the driver's use
@@ -140,6 +142,7 @@ typedef void (*rpmsg_rx_cb_t)(struct rpmsg_channel *, void *, int, void *, u32);
  */
 struct rpmsg_endpoint {
 	struct rpmsg_channel *rpdev;
+	struct kref refcount;
 	rpmsg_rx_cb_t cb;
 	u32 addr;
 	void *priv;