[dpdk-dev] [PATCH v2 07/10] service: avoid race condition for MT unsafe service

[Phil Yang]

From: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>

There has possible that a MT unsafe service might get configured to
run on another core while the service is running currently. This
might result in the MT unsafe service running on multiple cores
simultaneously. Use 'execute_lock' always when the service is
MT unsafe.

Fixes: e9139a32f6e8 ("service: add function to run on app lcore")
Cc: stable at dpdk.org

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Reviewed-by: Phil Yang <phil.yang at arm.com>
Reviewed-by: Gavin Hu <gavin.hu at arm.com>
---
 lib/librte_eal/common/rte_service.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 6990dc2..b37fc56 100644
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -50,6 +50,10 @@ struct rte_service_spec_impl {
 	uint8_t internal_flags;
 
 	/* per service statistics */
+	/* Indicates how many cores the service is mapped to run on.
+	 * It does not indicate the number of cores the service is running
+	 * on currently.
+	 */
 	rte_atomic32_t num_mapped_cores;
 	uint64_t calls;
 	uint64_t cycles_spent;
@@ -367,12 +371,7 @@ service_run(uint32_t i, struct core_state *cs, uint64_t service_mask,
 
 	cs->service_active_on_lcore[i] = 1;
 
-	/* check do we need cmpset, if MT safe or <= 1 core
-	 * mapped, atomic ops are not required.
-	 */
-	const int use_atomics = (service_mt_safe(s) == 0) &&
-				(rte_atomic32_read(&s->num_mapped_cores) > 1);
-	if (use_atomics) {
+	if (service_mt_safe(s) == 0) {
 		if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1))
 			return -EBUSY;
 
-- 
2.7.4