[PATCH v3 3/7] util/oslib-posix: Introduce and use MemsetContext for touch_all_pages()

[David Hildenbrand]

Let's minimize the number of global variables to prepare for
os_mem_prealloc() getting called concurrently and make the code a bit
easier to read.

The only consumer that really needs a global variable is the sigbus
handler, which will require protection via a mutex in the future either way
as we cannot concurrently mess with the SIGBUS handler.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 util/oslib-posix.c | 73 +++++++++++++++++++++++++++++-----------------
 1 file changed, 47 insertions(+), 26 deletions(-)

diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index cb89e07770..cf2ead54ad 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -73,21 +73,30 @@
 
 #define MAX_MEM_PREALLOC_THREAD_COUNT 16
 
+struct MemsetThread;
+
+typedef struct MemsetContext {
+    bool all_threads_created;
+    bool any_thread_failed;
+    struct MemsetThread *threads;
+    int num_threads;
+} MemsetContext;
+
 struct MemsetThread {
     char *addr;
     size_t numpages;
     size_t hpagesize;
     QemuThread pgthread;
     sigjmp_buf env;
+    MemsetContext *context;
 };
 typedef struct MemsetThread MemsetThread;
 
-static MemsetThread *memset_thread;
-static int memset_num_threads;
+/* used by sigbus_handler() */
+static MemsetContext *sigbus_memset_context;
 
 static QemuMutex page_mutex;
 static QemuCond page_cond;
-static bool threads_created_flag;
 
 int qemu_get_thread_id(void)
 {
@@ -438,10 +447,13 @@ const char *qemu_get_exec_dir(void)
 static void sigbus_handler(int signal)
 {
     int i;
-    if (memset_thread) {
-        for (i = 0; i < memset_num_threads; i++) {
-            if (qemu_thread_is_self(&memset_thread[i].pgthread)) {
-                siglongjmp(memset_thread[i].env, 1);
+
+    if (sigbus_memset_context) {
+        for (i = 0; i < sigbus_memset_context->num_threads; i++) {
+            MemsetThread *thread = &sigbus_memset_context->threads[i];
+
+            if (qemu_thread_is_self(&thread->pgthread)) {
+                siglongjmp(thread->env, 1);
             }
         }
     }
@@ -459,7 +471,7 @@ static void *do_touch_pages(void *arg)
      * clearing until all threads have been created.
      */
     qemu_mutex_lock(&page_mutex);
-    while(!threads_created_flag){
+    while (!memset_args->context->all_threads_created) {
         qemu_cond_wait(&page_cond, &page_mutex);
     }
     qemu_mutex_unlock(&page_mutex);
@@ -502,7 +514,7 @@ static void *do_madv_populate_write_pages(void *arg)
 
     /* See do_touch_pages(). */
     qemu_mutex_lock(&page_mutex);
-    while (!threads_created_flag) {
+    while (!memset_args->context->all_threads_created) {
         qemu_cond_wait(&page_cond, &page_mutex);
     }
     qemu_mutex_unlock(&page_mutex);
@@ -529,6 +541,9 @@ static int touch_all_pages(char *area, size_t hpagesize, 
size_t numpages,
                            int smp_cpus, bool use_madv_populate_write)
 {
     static gsize initialized = 0;
+    MemsetContext context = {
+        .num_threads = get_memset_num_threads(smp_cpus),
+    };
     size_t numpages_per_thread, leftover;
     void *(*touch_fn)(void *);
     int ret = 0, i = 0;
@@ -546,35 +561,41 @@ static int touch_all_pages(char *area, size_t hpagesize, 
size_t numpages,
         touch_fn = do_touch_pages;
     }
 
-    threads_created_flag = false;
-    memset_num_threads = get_memset_num_threads(smp_cpus);
-    memset_thread = g_new0(MemsetThread, memset_num_threads);
-    numpages_per_thread = numpages / memset_num_threads;
-    leftover = numpages % memset_num_threads;
-    for (i = 0; i < memset_num_threads; i++) {
-        memset_thread[i].addr = addr;
-        memset_thread[i].numpages = numpages_per_thread + (i < leftover);
-        memset_thread[i].hpagesize = hpagesize;
-        qemu_thread_create(&memset_thread[i].pgthread, "touch_pages",
-                           touch_fn, &memset_thread[i],
+    context.threads = g_new0(MemsetThread, context.num_threads);
+    numpages_per_thread = numpages / context.num_threads;
+    leftover = numpages % context.num_threads;
+    for (i = 0; i < context.num_threads; i++) {
+        context.threads[i].addr = addr;
+        context.threads[i].numpages = numpages_per_thread + (i < leftover);
+        context.threads[i].hpagesize = hpagesize;
+        context.threads[i].context = &context;
+        qemu_thread_create(&context.threads[i].pgthread, "touch_pages",
+                           touch_fn, &context.threads[i],
                            QEMU_THREAD_JOINABLE);
-        addr += memset_thread[i].numpages * hpagesize;
+        addr += context.threads[i].numpages * hpagesize;
+    }
+
+    if (!use_madv_populate_write) {
+        sigbus_memset_context = &context;
     }
 
     qemu_mutex_lock(&page_mutex);
-    threads_created_flag = true;
+    context.all_threads_created = true;
     qemu_cond_broadcast(&page_cond);
     qemu_mutex_unlock(&page_mutex);
 
-    for (i = 0; i < memset_num_threads; i++) {
-        int tmp = (uintptr_t)qemu_thread_join(&memset_thread[i].pgthread);
+    for (i = 0; i < context.num_threads; i++) {
+        int tmp = (uintptr_t)qemu_thread_join(&context.threads[i].pgthread);
 
         if (tmp) {
             ret = tmp;
         }
     }
-    g_free(memset_thread);
-    memset_thread = NULL;
+
+    if (!use_madv_populate_write) {
+        sigbus_memset_context = NULL;
+    }
+    g_free(context.threads);
 
     return ret;
 }
-- 
2.31.1