IB/core: Protect against concurrent access to hardware stats

Currently access to hardware stats buffer isn't protected, this can
result in multiple writes and reads at the same time to the same
memory location. This can lead to providing an incorrect value to
the user. Add a mutex to protect against it.

Fixes: b40f4757da ("IB/core: Make device counter infrastructure dynamic")
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/rdma/ib_verbs.h

@@ -470,6 +470,9 @@ enum ib_port_speed {
 
 /**
  * struct rdma_hw_stats
+ * @lock - Mutex to protect parallel write access to lifespan and values
+ *    of counters, which are 64bits and not guaranteeed to be written
+ *    atomicaly on 32bits systems.
  * @timestamp - Used by the core code to track when the last update was
  * @lifespan - Used by the core code to determine how old the counters
  *   should be before being updated again.  Stored in jiffies, defaults
@@ -485,6 +488,7 @@ enum ib_port_speed {
  *   filled in by the drivers get_stats routine
  */
 struct rdma_hw_stats {
+	struct mutex	lock; /* Protect lifespan and values[] */
 	unsigned long	timestamp;
 	unsigned long	lifespan;
 	const char * const *names;