[dpdk-dev] [PATCH v2 08/15] service: fix and refactor atomic service accesses

[Harry van Haaren]

This commit fixes an issue in the service runner function,
where the atomic value was not cleared on exiting the service
function. This resulted in future attempts to run the service
to appear like the function was running, however it was in
reality deadlocked.

This commit refactors the atomic handling to be more readable,
by splitting the implementation code into a new static inline
function. The remaining flow control of atomics in the existing
function is refactored for readability.

Fixes: 21698354c832 ("service: introduce service cores concept")

Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
---
 doc/guides/rel_notes/release_17_11.rst |  7 ++++++
 lib/librte_eal/common/rte_service.c    | 45 ++++++++++++++++++++--------------
 2 files changed, 33 insertions(+), 19 deletions(-)

diff --git a/doc/guides/rel_notes/release_17_11.rst b/doc/guides/rel_notes/release_17_11.rst
index 170f4f9..6e6ba1c 100644
--- a/doc/guides/rel_notes/release_17_11.rst
+++ b/doc/guides/rel_notes/release_17_11.rst
@@ -65,6 +65,13 @@ Resolved Issues
 EAL
 ~~~
 
+* **Service core fails to call service callback due to atomic lock**
+
+  In a specific configuration of multi-thread unsafe services and service
+  cores, a service core previously did not correctly release the atomic lock
+  on the service. This would result in the cores polling the service, but it
+  looked like another thread was executing the service callback. The logic for
+  atomic locking of the services has been fixed and refactored for readability.
 
 Drivers
 ~~~~~~~
diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 1bfd149..6291c0c 100644
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -296,6 +296,23 @@ rte_service_runstate_get(uint32_t id)
 	return (s->runstate == RUNSTATE_RUNNING) && (s->num_mapped_cores > 0);
 }
 
+static inline void
+rte_service_runner_do_callback(struct rte_service_spec_impl *s,
+			       struct core_state *cs, uint32_t service_idx)
+{
+	void *userdata = s->spec.callback_userdata;
+
+	if (service_stats_enabled(s)) {
+		uint64_t start = rte_rdtsc();
+		s->spec.callback(userdata);
+		uint64_t end = rte_rdtsc();
+		s->cycles_spent += end - start;
+		cs->calls_per_service[service_idx]++;
+		s->calls++;
+	} else
+		s->spec.callback(userdata);
+}
+
 static int32_t
 rte_service_runner_func(void *arg)
 {
@@ -315,26 +332,16 @@ rte_service_runner_func(void *arg)
 			/* check do we need cmpset, if MT safe or <= 1 core
 			 * mapped, atomic ops are not required.
 			 */
-			const int need_cmpset = !((service_mt_safe(s) == 0) &&
-						(s->num_mapped_cores > 1));
-			uint32_t *lock = (uint32_t *)&s->execute_lock;
-
-			if (need_cmpset || rte_atomic32_cmpset(lock, 0, 1)) {
-				void *userdata = s->spec.callback_userdata;
-
-				if (service_stats_enabled(s)) {
-					uint64_t start = rte_rdtsc();
-					s->spec.callback(userdata);
-					uint64_t end = rte_rdtsc();
-					s->cycles_spent += end - start;
-					cs->calls_per_service[i]++;
-					s->calls++;
-				} else
-					s->spec.callback(userdata);
-
-				if (need_cmpset)
+			const int use_atomics = (service_mt_safe(s) == 0) &&
+						(s->num_mapped_cores > 1);
+			if (use_atomics) {
+				uint32_t *lock = (uint32_t *)&s->execute_lock;
+				if (rte_atomic32_cmpset(lock, 0, 1)) {
+					rte_service_runner_do_callback(s, cs, i);
 					rte_atomic32_clear(&s->execute_lock);
-			}
+				}
+			} else
+				rte_service_runner_do_callback(s, cs, i);
 		}
 
 		rte_smp_rmb();
-- 
2.7.4