SUNRPC: serialize iostats updates

Occasionally mountstats reports a negative retransmission rate.
Ensure that two RPCs completing concurrently don't confuse the sums
in the transport's op_metrics array.

Since pNFS filelayout can invoke rpc_count_iostats() on another
transport from xprt_release(), we can't rely on simply holding the
transport_lock in xprt_release(). There's nothing for it but hard
serialization. One spin lock per RPC operation should make this as
painless as it can be.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

diff --git a/include/linux/sunrpc/metrics.h b/include/linux/sunrpc/metrics.h
index 1565bbe86d51e77c2323ca26a04bbad8a35b9f22..eecb5a71e6c0e4362a502a608ebfa179c975f808 100644 (file)
--- a/include/linux/sunrpc/metrics.h
+++ b/include/linux/sunrpc/metrics.h
@@ -27,10 +27,13 @@
 
 #include <linux/seq_file.h>
 #include <linux/ktime.h>
+#include <linux/spinlock.h>
 
 #define RPC_IOSTATS_VERS       "1.0"
 
 struct rpc_iostats {
+       spinlock_t              om_lock;
+
        /*
         * These counters give an idea about how many request
         * transmissions are required, on average, to complete that

diff --git a/net/sunrpc/stats.c b/net/sunrpc/stats.c
index 54530490944e8a9bbb49e12e1d620f183b0e012d..9711a155bc50071995402518d1ddd56a78b24a2a 100644 (file)
--- a/net/sunrpc/stats.c
+++ b/net/sunrpc/stats.c
@@ -116,7 +116,15 @@ EXPORT_SYMBOL_GPL(svc_seq_show);
  */
 struct rpc_iostats *rpc_alloc_iostats(struct rpc_clnt *clnt)
 {
-       return kcalloc(clnt->cl_maxproc, sizeof(struct rpc_iostats), GFP_KERNEL);
+       struct rpc_iostats *stats;
+       int i;
+
+       stats = kcalloc(clnt->cl_maxproc, sizeof(*stats), GFP_KERNEL);
+       if (stats) {
+               for (i = 0; i < clnt->cl_maxproc; i++)
+                       spin_lock_init(&stats[i].om_lock);
+       }
+       return stats;
 }
 EXPORT_SYMBOL_GPL(rpc_alloc_iostats);
 
@@ -135,20 +143,21 @@ EXPORT_SYMBOL_GPL(rpc_free_iostats);
  * rpc_count_iostats - tally up per-task stats
  * @task: completed rpc_task
  * @stats: array of stat structures
- *
- * Relies on the caller for serialization.
  */
 void rpc_count_iostats(const struct rpc_task *task, struct rpc_iostats *stats)
 {
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_iostats *op_metrics;
-       ktime_t delta;
+       ktime_t delta, now;
 
        if (!stats || !req)
                return;
 
+       now = ktime_get();
        op_metrics = &stats[task->tk_msg.rpc_proc->p_statidx];
 
+       spin_lock(&op_metrics->om_lock);
+
        op_metrics->om_ops++;
        op_metrics->om_ntrans += req->rq_ntrans;
        op_metrics->om_timeouts += task->tk_timeouts;
@@ -161,8 +170,10 @@ void rpc_count_iostats(const struct rpc_task *task, struct rpc_iostats *stats)
 
        op_metrics->om_rtt = ktime_add(op_metrics->om_rtt, req->rq_rtt);
 
-       delta = ktime_sub(ktime_get(), task->tk_start);
+       delta = ktime_sub(now, task->tk_start);
        op_metrics->om_execute = ktime_add(op_metrics->om_execute, delta);
+
+       spin_unlock(&op_metrics->om_lock);
 }
 EXPORT_SYMBOL_GPL(rpc_count_iostats);