[perf-counters] Declare shared data header type directly after creation

Fix the following bug : shared_data_find_room return twice the same memory region because it was not marked as "in use" by setting the header.ftype value.
This bug is triggered when we want to create a new shared area (for example a new FTYPE_INSTANCE area) while creating another area (for example a new FTYPE_CATEGORY).

diff --git a/mono/metadata/mono-perfcounters.c b/mono/metadata/mono-perfcounters.c
index ed29049a191067d65ae4176945a012ff8aebe5ec..7479a564360b9a935ed3dd9e1b6c5e75cc581add 100644 (file)
--- a/mono/metadata/mono-perfcounters.c
+++ b/mono/metadata/mono-perfcounters.c
@@ -478,9 +478,10 @@ perfctr_type_compress (int type)
        return 2;
 }
 
-static unsigned char*
-shared_data_find_room (int size)
+static SharedHeader*
+shared_data_reserve_room (int size, int ftype)
 {
+       SharedHeader* header;
        unsigned char *p = (unsigned char *)shared_area + shared_area->data_start;
        unsigned char *end = (unsigned char *)shared_area + shared_area->size;
 
@@ -490,7 +491,7 @@ shared_data_find_room (int size)
                unsigned short *next;
                if (*p == FTYPE_END) {
                        if (size < (end - p))
-                               return p;
+                               goto res;
                        return NULL;
                }
                if (p + 4 > end)
@@ -499,12 +500,20 @@ shared_data_find_room (int size)
                if (*p == FTYPE_DELETED) {
                        /* we reuse only if it's the same size */
                        if (*next == size) {
-                               return p;
+                               goto res;
                        }
                }
                p += *next;
        }
        return NULL;
+
+res:
+       header = (SharedHeader*)p;
+       header->ftype = ftype;
+       header->extra = 0; /* data_offset could overflow here, so we leave this field unused */
+       header->size = size;
+
+       return header;
 }
 
 typedef gboolean (*SharedFunc) (SharedHeader *header, void *data);
@@ -1144,7 +1153,6 @@ static SharedInstance*
 custom_get_instance (SharedCategory *cat, SharedCounter *scounter, MonoString* instance)
 {
        SharedInstance* inst;
-       unsigned char *ptr;
        char *p;
        int size, data_offset;
        char *name;
@@ -1158,22 +1166,18 @@ custom_get_instance (SharedCategory *cat, SharedCounter *scounter, MonoString* i
        data_offset = size;
        size += (sizeof (guint64) * cat->num_counters);
        perfctr_lock ();
-       ptr = shared_data_find_room (size);
-       if (!ptr) {
+       inst = (SharedInstance*) shared_data_reserve_room (size, FTYPE_INSTANCE);
+       if (!inst) {
                perfctr_unlock ();
                g_free (name);
                return NULL;
        }
-       inst = (SharedInstance*)ptr;
-       inst->header.extra = 0; /* data_offset could overflow here, so we leave this field unused */
-       inst->header.size = size;
        inst->category_offset = (char*)cat - (char*)shared_area;
        cat->num_instances++;
        /* now copy the variable data */
        p = inst->instance_name;
        strcpy (p, name);
        p += strlen (name) + 1;
-       inst->header.ftype = FTYPE_INSTANCE;
        perfctr_unlock ();
        g_free (name);
 
@@ -1384,7 +1388,6 @@ mono_perfcounter_create (MonoString *category, MonoString *help, int type, MonoA
        char *name = NULL;
        char *chelp = NULL;
        char **counter_info = NULL;
-       unsigned char *ptr;
        char *p;
        SharedCategory *cat;
 
@@ -1420,14 +1423,11 @@ mono_perfcounter_create (MonoString *category, MonoString *help, int type, MonoA
        if (size > 65535)
                goto failure;
        perfctr_lock ();
-       ptr = shared_data_find_room (size);
-       if (!ptr) {
+       cat = (SharedCategory*) shared_data_reserve_room (size, FTYPE_CATEGORY);
+       if (!cat) {
                perfctr_unlock ();
                goto failure;
        }
-       cat = (SharedCategory*)ptr;
-       cat->header.extra = type;
-       cat->header.size = size;
        cat->num_counters = num_counters;
        cat->counters_data_size = counters_data_size;
        /* now copy the vaiable data */
@@ -1446,7 +1446,6 @@ mono_perfcounter_create (MonoString *category, MonoString *help, int type, MonoA
                strcpy (p, counter_info [i * 2 + 1]);
                p += strlen (counter_info [i * 2 + 1]) + 1;
        }
-       cat->header.ftype = FTYPE_CATEGORY;
 
        perfctr_unlock ();
        result = TRUE;