[dpdk-stable] patch 'service: fix race condition for MT unsafe service' has been queued to LTS release 18.11.9

[Kevin Traynor]

Hi,

FYI, your patch has been queued to LTS release 18.11.9

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 06/10/20. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Queued patches are on a temporary branch at:
https://github.com/kevintraynor/dpdk-stable-queue

This queued commit can be viewed at:
https://github.com/kevintraynor/dpdk-stable-queue/commit/817639c78342003d5d3d675f6bc0eca05ee2c6be

Thanks.

Kevin.

---
>From 817639c78342003d5d3d675f6bc0eca05ee2c6be Mon Sep 17 00:00:00 2001
From: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Date: Wed, 6 May 2020 23:27:59 +0800
Subject: [PATCH] service: fix race condition for MT unsafe service

[ upstream commit 18cae99cb9096abe0f33b43e51eb8b781e8a5ff9 ]

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.

If the service is known to be mapped on a single lcore,
setting the service capability to MT safe will avoid taking
the lock and improve the performance.

Fixes: e9139a32f6e8 ("service: add function to run on app lcore")

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Reviewed-by: Phil Yang <phil.yang at arm.com>
Acked-by: Harry van Haaren <harry.van.haaren at intel.com>
---
 lib/librte_eal/common/include/rte_service.h           |  8 ++++++--
 lib/librte_eal/common/include/rte_service_component.h |  6 +++++-
 lib/librte_eal/common/rte_service.c                   | 11 +++++------
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/lib/librte_eal/common/include/rte_service.h b/lib/librte_eal/common/include/rte_service.h
index 11f673503b..21002209bc 100644
--- a/lib/librte_eal/common/include/rte_service.h
+++ b/lib/librte_eal/common/include/rte_service.h
@@ -105,10 +105,14 @@ int32_t rte_service_probe_capability(uint32_t id, uint32_t capability);
  * function enables or disables *lcore* to run *service_id*.
  *
- * If multiple cores are enabled on a service, an atomic is used to ensure that
- * only one cores runs the service at a time. The exception to this is when
+ * If multiple cores are enabled on a service, a lock is used to ensure that
+ * only one core runs the service at a time. The exception to this is when
  * a service indicates that it is multi-thread safe by setting the capability
  * called RTE_SERVICE_CAP_MT_SAFE. With the multi-thread safe capability set,
  * the service function can be run on multiple threads at the same time.
  *
+ * If the service is known to be mapped to a single lcore, setting the
+ * capability of the service to RTE_SERVICE_CAP_MT_SAFE can achieve
+ * better performance by avoiding the use of lock.
+ *
  * @param service_id the service to apply the lcore to
  * @param lcore The lcore that will be mapped to service
diff --git a/lib/librte_eal/common/include/rte_service_component.h b/lib/librte_eal/common/include/rte_service_component.h
index c12adbc256..259e3182d8 100644
--- a/lib/librte_eal/common/include/rte_service_component.h
+++ b/lib/librte_eal/common/include/rte_service_component.h
@@ -44,5 +44,5 @@ struct rte_service_spec {
  * Register a new service.
  *
- * A service represents a component that the requires CPU time periodically to
+ * A service represents a component that requires CPU time periodically to
  * achieve its purpose.
  *
@@ -57,4 +57,8 @@ struct rte_service_spec {
  * component is ready to be executed.
  *
+ * If the service is known to be mapped to a single lcore, setting the
+ * capability of the service to RTE_SERVICE_CAP_MT_SAFE can achieve
+ * better performance.
+ *
  * @param spec The specification of the service to register
  * @param[out] service_id A pointer to a uint32_t, which will be filled in
diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 5e757fbd19..e71e1efaa8 100644
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -50,4 +50,8 @@ struct rte_service_spec_impl {
 
 	/* 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;
@@ -370,10 +374,5 @@ 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;
-- 
2.21.3

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2020-06-05 19:20:51.965166867 +0100
+++ 0019-service-fix-race-condition-for-MT-unsafe-service.patch	2020-06-05 19:20:50.740042404 +0100
@@ -1 +1 @@
-From 18cae99cb9096abe0f33b43e51eb8b781e8a5ff9 Mon Sep 17 00:00:00 2001
+From 817639c78342003d5d3d675f6bc0eca05ee2c6be Mon Sep 17 00:00:00 2001
@@ -5,0 +6,2 @@
+[ upstream commit 18cae99cb9096abe0f33b43e51eb8b781e8a5ff9 ]
+
@@ -16 +17,0 @@
-Cc: stable at dpdk.org
@@ -22,3 +23,3 @@
- lib/librte_eal/common/rte_service.c            | 11 +++++------
- lib/librte_eal/include/rte_service.h           |  8 ++++++--
- lib/librte_eal/include/rte_service_component.h |  6 +++++-
+ lib/librte_eal/common/include/rte_service.h           |  8 ++++++--
+ lib/librte_eal/common/include/rte_service_component.h |  6 +++++-
+ lib/librte_eal/common/rte_service.c                   | 11 +++++------
@@ -27,29 +28,4 @@
-diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
-index 70d17a5d79..b8c465eb96 100644
---- a/lib/librte_eal/common/rte_service.c
-+++ b/lib/librte_eal/common/rte_service.c
-@@ -51,4 +51,8 @@ struct rte_service_spec_impl {
- 
- 	/* 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;
-@@ -371,10 +375,5 @@ 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;
-diff --git a/lib/librte_eal/include/rte_service.h b/lib/librte_eal/include/rte_service.h
-index d8701dd4cf..3a1c735c58 100644
---- a/lib/librte_eal/include/rte_service.h
-+++ b/lib/librte_eal/include/rte_service.h
+diff --git a/lib/librte_eal/common/include/rte_service.h b/lib/librte_eal/common/include/rte_service.h
+index 11f673503b..21002209bc 100644
+--- a/lib/librte_eal/common/include/rte_service.h
++++ b/lib/librte_eal/common/include/rte_service.h
@@ -73,4 +49,4 @@
-diff --git a/lib/librte_eal/include/rte_service_component.h b/lib/librte_eal/include/rte_service_component.h
-index 16eab79eea..b75aba11b9 100644
---- a/lib/librte_eal/include/rte_service_component.h
-+++ b/lib/librte_eal/include/rte_service_component.h
+diff --git a/lib/librte_eal/common/include/rte_service_component.h b/lib/librte_eal/common/include/rte_service_component.h
+index c12adbc256..259e3182d8 100644
+--- a/lib/librte_eal/common/include/rte_service_component.h
++++ b/lib/librte_eal/common/include/rte_service_component.h
@@ -92,0 +69,25 @@
+diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
+index 5e757fbd19..e71e1efaa8 100644
+--- a/lib/librte_eal/common/rte_service.c
++++ b/lib/librte_eal/common/rte_service.c
+@@ -50,4 +50,8 @@ struct rte_service_spec_impl {
+ 
+ 	/* 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;
+@@ -370,10 +374,5 @@ 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;