mem: provide thread-unsafe memseg list walk variant

Sometimes, user code needs to walk memseg list while being inside
a memory-related callback. Rather than making everyone copy around
the same iteration code and depending on DPDK internals, provide an
official way to do memseg_list_walk() inside callbacks.

Also, remove existing reimplementation from memalloc code and use
the new API instead.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>

lib/librte_eal/common/eal_common_memory.c

@@ -513,14 +513,11 @@ rte_memseg_walk(rte_memseg_walk_t func, void *arg)
 }
 
 int __rte_experimental
-rte_memseg_list_walk(rte_memseg_list_walk_t func, void *arg)
+rte_memseg_list_walk_thread_unsafe(rte_memseg_list_walk_t func, void *arg)
 {
 	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 	int i, ret = 0;
 
-	/* do not allow allocations/frees/init while we iterate */
-	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
-
 	for (i = 0; i < RTE_MAX_MEMSEG_LISTS; i++) {
 		struct rte_memseg_list *msl = &mcfg->memsegs[i];
 
@@ -528,17 +525,23 @@ rte_memseg_list_walk(rte_memseg_list_walk_t func, void *arg)
 			continue;
 
 		ret = func(msl, arg);
-		if (ret < 0) {
-			ret = -1;
-			goto out;
-		}
-		if (ret > 0) {
-			ret = 1;
-			goto out;
-		}
+		if (ret)
+			return ret;
 	}
-out:
+	return 0;
+}
+
+int __rte_experimental
+rte_memseg_list_walk(rte_memseg_list_walk_t func, void *arg)
+{
+	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
+	int ret = 0;
+
+	/* do not allow allocations/frees/init while we iterate */
+	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
+	ret = rte_memseg_list_walk_thread_unsafe(func, arg);
 	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
+
 	return ret;
 }
 

lib/librte_eal/common/include/rte_memory.h

@@ -299,6 +299,24 @@ rte_memseg_walk_thread_unsafe(rte_memseg_walk_t func, void *arg);
 int __rte_experimental
 rte_memseg_contig_walk_thread_unsafe(rte_memseg_contig_walk_t func, void *arg);
 
+/**
+ * Walk each allocated memseg list without performing any locking.
+ *
+ * @note This function does not perform any locking, and is only safe to call
+ *       from within memory-related callback functions.
+ *
+ * @param func
+ *   Iterator function
+ * @param arg
+ *   Argument passed to iterator
+ * @return
+ *   0 if walked over the entire list
+ *   1 if stopped by the user
+ *   -1 if user function reported error
+ */
+int __rte_experimental
+rte_memseg_list_walk_thread_unsafe(rte_memseg_list_walk_t func, void *arg);
+
 /**
  * Dump the physical memory layout to a file.
  *

lib/librte_eal/linuxapp/eal/eal_memalloc.c

@@ -172,32 +172,6 @@ get_file_size(int fd)
 	return st.st_size;
 }
 
-/* we cannot use rte_memseg_list_walk() here because we will be holding a
- * write lock whenever we enter every function in this file, however copying
- * the same iteration code everywhere is not ideal as well. so, use a lockless
- * copy of memseg list walk here.
- */
-static int
-memseg_list_walk_thread_unsafe(rte_memseg_list_walk_t func, void *arg)
-{
-	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
-	int i, ret = 0;
-
-	for (i = 0; i < RTE_MAX_MEMSEG_LISTS; i++) {
-		struct rte_memseg_list *msl = &mcfg->memsegs[i];
-
-		if (msl->base_va == NULL)
-			continue;
-
-		ret = func(msl, arg);
-		if (ret < 0)
-			return -1;
-		if (ret > 0)
-			return 1;
-	}
-	return 0;
-}
-
 /* returns 1 on successful lock, 0 on unsuccessful lock, -1 on error */
 static int lock(int fd, int type)
 {
@@ -900,7 +874,8 @@ eal_memalloc_alloc_seg_bulk(struct rte_memseg **ms, int n_segs, size_t page_sz,
 	wa.socket = socket;
 	wa.segs_allocated = 0;
 
-	ret = memseg_list_walk_thread_unsafe(alloc_seg_walk, &wa);
+	/* memalloc is locked, so it's safe to use thread-unsafe version */
+	ret = rte_memseg_list_walk_thread_unsafe(alloc_seg_walk, &wa);
 	if (ret == 0) {
 		RTE_LOG(ERR, EAL, "%s(): couldn't find suitable memseg_list\n",
 			__func__);
@@ -965,7 +940,10 @@ eal_memalloc_free_seg_bulk(struct rte_memseg **ms, int n_segs)
 		wa.ms = cur;
 		wa.hi = hi;
 
-		walk_res = memseg_list_walk_thread_unsafe(free_seg_walk, &wa);
+		/* memalloc is locked, so it's safe to use thread-unsafe version
+		 */
+		walk_res = rte_memseg_list_walk_thread_unsafe(free_seg_walk,
+				&wa);
 		if (walk_res == 1)
 			continue;
 		if (walk_res == 0)
@@ -1252,7 +1230,8 @@ eal_memalloc_sync_with_primary(void)
 	if (rte_eal_process_type() == RTE_PROC_PRIMARY)
 		return 0;
 
-	if (memseg_list_walk_thread_unsafe(sync_walk, NULL))
+	/* memalloc is locked, so it's safe to call thread-unsafe version */
+	if (rte_memseg_list_walk_thread_unsafe(sync_walk, NULL))
 		return -1;
 	return 0;
 }

lib/librte_eal/rte_eal_version.map

@@ -294,6 +294,7 @@ EXPERIMENTAL {
 	rte_memseg_contig_walk;
 	rte_memseg_contig_walk_thread_unsafe;
 	rte_memseg_list_walk;
+	rte_memseg_list_walk_thread_unsafe;
 	rte_memseg_walk;
 	rte_memseg_walk_thread_unsafe;
 	rte_mp_action_register;