[PULL v2 29/55] util/oslib-posix: Let touch_all_pages() return an error

["Michael S. Tsirkin" <mst@redhat.com>]

From: David Hildenbrand <david@redhat.com>

Let's prepare touch_all_pages() for returning differing errors. Return
an error from the thread and report the last processed error.

Translate SIGBUS to -EFAULT, as a SIGBUS can mean all different kind of
things (memory error, read error, out of memory). When allocating memory
fails via the current SIGBUS-based mechanism, we'll get:
    os_mem_prealloc: preallocating memory failed: Bad address

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211217134611.31172-2-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 util/oslib-posix.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index e8bdb02e1d..b146beef78 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -84,7 +84,6 @@ typedef struct MemsetThread MemsetThread;
 
 static MemsetThread *memset_thread;
 static int memset_num_threads;
-static bool memset_thread_failed;
 
 static QemuMutex page_mutex;
 static QemuCond page_cond;
@@ -452,6 +451,7 @@ static void *do_touch_pages(void *arg)
 {
     MemsetThread *memset_args = (MemsetThread *)arg;
     sigset_t set, oldset;
+    int ret = 0;
 
     /*
      * On Linux, the page faults from the loop below can cause mmap_sem
@@ -470,7 +470,7 @@ static void *do_touch_pages(void *arg)
     pthread_sigmask(SIG_UNBLOCK, &set, &oldset);
 
     if (sigsetjmp(memset_args->env, 1)) {
-        memset_thread_failed = true;
+        ret = -EFAULT;
     } else {
         char *addr = memset_args->addr;
         size_t numpages = memset_args->numpages;
@@ -494,7 +494,7 @@ static void *do_touch_pages(void *arg)
         }
     }
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
-    return NULL;
+    return (void *)(uintptr_t)ret;
 }
 
 static inline int get_memset_num_threads(int smp_cpus)
@@ -509,13 +509,13 @@ static inline int get_memset_num_threads(int smp_cpus)
     return ret;
 }
 
-static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
-                            int smp_cpus)
+static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
+                           int smp_cpus)
 {
     static gsize initialized = 0;
     size_t numpages_per_thread, leftover;
+    int ret = 0, i = 0;
     char *addr = area;
-    int i = 0;
 
     if (g_once_init_enter(&initialized)) {
         qemu_mutex_init(&page_mutex);
@@ -523,7 +523,6 @@ static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
         g_once_init_leave(&initialized, 1);
     }
 
-    memset_thread_failed = false;
     threads_created_flag = false;
     memset_num_threads = get_memset_num_threads(smp_cpus);
     memset_thread = g_new0(MemsetThread, memset_num_threads);
@@ -545,12 +544,16 @@ static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
     qemu_mutex_unlock(&page_mutex);
 
     for (i = 0; i < memset_num_threads; i++) {
-        qemu_thread_join(&memset_thread[i].pgthread);
+        int tmp = (uintptr_t)qemu_thread_join(&memset_thread[i].pgthread);
+
+        if (tmp) {
+            ret = tmp;
+        }
     }
     g_free(memset_thread);
     memset_thread = NULL;
 
-    return memset_thread_failed;
+    return ret;
 }
 
 void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
@@ -573,9 +576,10 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
     }
 
     /* touch pages simultaneously */
-    if (touch_all_pages(area, hpagesize, numpages, smp_cpus)) {
-        error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
-            "pages available to allocate guest RAM");
+    ret = touch_all_pages(area, hpagesize, numpages, smp_cpus);
+    if (ret) {
+        error_setg_errno(errp, -ret,
+                         "os_mem_prealloc: preallocating memory failed");
     }
 
     ret = sigaction(SIGBUS, &oldact, NULL);
-- 
MST