[PATCH v3 1/7] eal: add helper to initialize process-shared mutex

[Stephen Hemminger <stephen@networkplumber.org>]

Drivers and libraries that place a pthread_mutex_t in shared memory
to coordinate primary and secondary DPDK processes must initialize
the mutex with PTHREAD_PROCESS_SHARED, otherwise behaviour is
undefined. Add an internal helper so this is done in one place rather
than copied into every driver.

Errors from the attribute calls are ignored: on platforms that do not
support cross-process mutex sharing the mutex still works within a
single process.

Bugzilla ID: 662
Cc: stable@dpdk.org

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/eal/include/rte_thread.h | 15 +++++++++++++++
 lib/eal/unix/rte_thread.c    | 12 ++++++++++++
 lib/eal/windows/rte_thread.c | 10 ++++++++++
 3 files changed, 37 insertions(+)

diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
index 8da9d4d3fb..27d5b9c594 100644
--- a/lib/eal/include/rte_thread.h
+++ b/lib/eal/include/rte_thread.h
@@ -3,6 +3,7 @@
  * Copyright (C) 2022 Microsoft Corporation
  */
 
+#include <pthread.h>
 #include <stdint.h>
 
 #include <rte_os.h>
@@ -463,6 +464,20 @@ int rte_thread_value_set(rte_thread_key key, const void *value);
  */
 void *rte_thread_value_get(rte_thread_key key);
 
+/**
+ * Initialize a pthread mutex for use in shared memory accessible by
+ * multiple DPDK processes.
+ *
+ * Sets PTHREAD_PROCESS_SHARED so the mutex can synchronize threads
+ * across DPDK primary and secondary processes when the mutex resides
+ * in shared memory (e.g. hugepage memory).
+ *
+ * @param mutex
+ *   The mutex to initialize.
+ */
+__rte_internal
+void rte_thread_mutex_init_shared(pthread_mutex_t *mutex);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 950c0848ba..f3a6bd2ad3 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -419,3 +419,15 @@ rte_thread_get_affinity_by_id(rte_thread_t thread_id,
 	return pthread_getaffinity_np((pthread_t)thread_id.opaque_id,
 		sizeof(*cpuset), cpuset);
 }
+
+RTE_EXPORT_INTERNAL_SYMBOL(rte_thread_mutex_init_shared)
+void
+rte_thread_mutex_init_shared(pthread_mutex_t *mutex)
+{
+	pthread_mutexattr_t attr;
+
+	pthread_mutexattr_init(&attr);
+	pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
+	pthread_mutex_init(mutex, &attr);
+	pthread_mutexattr_destroy(&attr);
+}
diff --git a/lib/eal/windows/rte_thread.c b/lib/eal/windows/rte_thread.c
index 85e5a57346..19bb9ed61d 100644
--- a/lib/eal/windows/rte_thread.c
+++ b/lib/eal/windows/rte_thread.c
@@ -621,3 +621,13 @@ rte_thread_get_affinity_by_id(rte_thread_t thread_id,
 	}
 	return ret;
 }
+
+/* Note: Windows does not have PTHREAD_PROCESS_SHARED
+ * and DPDK on Windows only supports single process model.
+ */
+RTE_EXPORT_INTERNAL_SYMBOL(rte_thread_mutex_init_shared)
+void
+rte_thread_mutex_init_shared(pthread_mutex_t *mutex)
+{
+	pthread_mutex_init(mutex, NULL);
+}
-- 
2.53.0