fix qemu exit on memory hotplug when allocation fails at prealloc time

When adding hostmem backend at runtime, QEMU might exit with error:
  "os_mem_prealloc: Insufficient free host memory pages available to allocate guest RAM"

It happens due to os_mem_prealloc() not handling errors gracefully.

Fix it by passing errp argument so that os_mem_prealloc() could
report error to callers and undo performed allocation when
os_mem_prealloc() fails.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1469008443-72059-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

backends/hostmem.c

@@ -203,6 +203,7 @@ static bool host_memory_backend_get_prealloc(Object *obj, Error **errp)
 static void host_memory_backend_set_prealloc(Object *obj, bool value,
                                              Error **errp)
 {
+    Error *local_err = NULL;
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
 
     if (backend->force_prealloc) {
@@ -223,7 +224,11 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
         void *ptr = memory_region_get_ram_ptr(&backend->mr);
         uint64_t sz = memory_region_size(&backend->mr);
 
-        os_mem_prealloc(fd, ptr, sz);
+        os_mem_prealloc(fd, ptr, sz, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
         backend->prealloc = true;
     }
 }
@@ -286,8 +291,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
     if (bc->alloc) {
         bc->alloc(backend, &local_err);
         if (local_err) {
-            error_propagate(errp, local_err);
+            goto out;
-            return;
         }
 
         ptr = memory_region_get_ram_ptr(&backend->mr);
@@ -343,9 +347,15 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
          * specified NUMA policy in place.
          */
         if (backend->prealloc) {
-            os_mem_prealloc(memory_region_get_fd(&backend->mr), ptr, sz);
+            os_mem_prealloc(memory_region_get_fd(&backend->mr), ptr, sz,
+                            &local_err);
+            if (local_err) {
+                goto out;
             }
         }
+    }
+out:
+    error_propagate(errp, local_err);
 }
 
 static bool

exec.c

@@ -1226,7 +1226,7 @@ static void *file_ram_alloc(RAMBlock *block,
     char *filename;
     char *sanitized_name;
     char *c;
-    void *area;
+    void *area = MAP_FAILED;
     int fd = -1;
     int64_t page_size;
 
@@ -1314,13 +1314,19 @@ static void *file_ram_alloc(RAMBlock *block,
     }
 
     if (mem_prealloc) {
-        os_mem_prealloc(fd, area, memory);
+        os_mem_prealloc(fd, area, memory, errp);
+        if (errp && *errp) {
+            goto error;
+        }
     }
 
     block->fd = fd;
     return area;
 
 error:
+    if (area != MAP_FAILED) {
+        qemu_ram_munmap(area, memory);
+    }
     if (unlink_on_error) {
         unlink(path);
     }

include/qemu/osdep.h

@@ -379,7 +379,7 @@ unsigned long qemu_getauxval(unsigned long type);
 
 void qemu_set_tty_echo(int fd, bool echo);
 
-void os_mem_prealloc(int fd, char *area, size_t sz);
+void os_mem_prealloc(int fd, char *area, size_t sz, Error **errp);
 
 int qemu_read_password(char *buf, int buf_size);
 

util/oslib-posix.c

@@ -318,7 +318,7 @@ static void sigbus_handler(int signal)
     siglongjmp(sigjump, 1);
 }
 
-void os_mem_prealloc(int fd, char *area, size_t memory)
+void os_mem_prealloc(int fd, char *area, size_t memory, Error **errp)
 {
     int ret;
     struct sigaction act, oldact;
@@ -330,8 +330,9 @@ void os_mem_prealloc(int fd, char *area, size_t memory)
 
     ret = sigaction(SIGBUS, &act, &oldact);
     if (ret) {
-        perror("os_mem_prealloc: failed to install signal handler");
+        error_setg_errno(errp, errno,
-        exit(1);
+            "os_mem_prealloc: failed to install signal handler");
+        return;
     }
 
     /* unblock SIGBUS */
@@ -340,9 +341,8 @@ void os_mem_prealloc(int fd, char *area, size_t memory)
     pthread_sigmask(SIG_UNBLOCK, &set, &oldset);
 
     if (sigsetjmp(sigjump, 1)) {
-        fprintf(stderr, "os_mem_prealloc: Insufficient free host memory "
+        error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
             "pages available to allocate guest RAM\n");
-        exit(1);
     } else {
         int i;
         size_t hpagesize = qemu_fd_getpagesize(fd);
@@ -352,15 +352,15 @@ void os_mem_prealloc(int fd, char *area, size_t memory)
         for (i = 0; i < numpages; i++) {
             memset(area + (hpagesize * i), 0, 1);
         }
+    }
 
     ret = sigaction(SIGBUS, &oldact, NULL);
     if (ret) {
+        /* Terminate QEMU since it can't recover from error */
         perror("os_mem_prealloc: failed to reinstall signal handler");
         exit(1);
     }
-
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
-    }
 }
 
 

util/oslib-win32.c

@@ -539,7 +539,7 @@ int getpagesize(void)
     return system_info.dwPageSize;
 }
 
-void os_mem_prealloc(int fd, char *area, size_t memory)
+void os_mem_prealloc(int fd, char *area, size_t memory, Error **errp)
 {
     int i;
     size_t pagesize = getpagesize();