Fix GC_proc_fd value in child process at fork (Solaris)

In case of PROC_VDB mode is initialized, GC_proc_fd contains a file
descriptor to "/proc/<pid>/pagedata".  After forking, the child
process has a different pid value, thus the old file descriptor
should be closed and the one with the updated file name should be
opened in turn.

* include/private/gc_priv.h [!GC_DISABLE_INCREMENTAL
&& CAN_HANDLE_FORK] (GC_dirty_update_child): Declare (as a function
or as a macro).
* os_dep.c [PROC_VDB] (GC_proc_fd): Initialize to -1 (instead of 0).
* os_dep.c [PROC_VDB] (proc_dirty_open_files): New static function
(part of code is moved from GC_dirty_init).
* os_dep.c [PROC_VDB && CAN_HANDLE_FORK] (GC_dirty_update_child): New
GC_INNER function.
* os_dep.c [PROC_VDB] (GC_dirty_init): Call proc_dirty_open_files().
* pthread_support.c [CAN_HANDLE_FORK && !GC_DISABLE_INCREMENTAL]
(fork_child_proc): Call GC_dirty_update_child().

3 files changed, 43 insertions, 12 deletions

diff --git a/include/private/gc_priv.h b/include/private/gc_priv.h
index 7b9bab1c..6685c07a 100644
--- a/include/private/gc_priv.h
+++ b/include/private/gc_priv.h
@@ -2416,6 +2416,17 @@ GC_EXTERN GC_bool GC_print_back_height;
                 /* pointer-free system call buffers in the heap are     */
                 /* not protected.                                       */
 
+# ifdef CAN_HANDLE_FORK
+#   if defined(PROC_VDB)
+      GC_INNER void GC_dirty_update_child(void);
+                /* Update pid-specific resources (like /proc file       */
+                /* descriptors) needed by the dirty bits implementation */
+                /* after fork in the child process.                     */
+#   else
+#     define GC_dirty_update_child() (void)0
+#   endif
+# endif /* CAN_HANDLE_FORK */
+
   GC_INNER GC_bool GC_dirty_init(void);
                 /* Returns true if dirty bits are maintained (otherwise */
                 /* it is OK to be called again if the client invokes    */
diff --git a/os_dep.c b/os_dep.c
index 45011595..eddf6f0f 100644
--- a/os_dep.c
+++ b/os_dep.c
@@ -3603,29 +3603,46 @@ STATIC void GC_protect_heap(void)
 # define INITIAL_BUF_SZ 16384
   STATIC size_t GC_proc_buf_size = INITIAL_BUF_SZ;
   STATIC char *GC_proc_buf = NULL;
-  STATIC int GC_proc_fd = 0;
+  STATIC int GC_proc_fd = -1;
 
-GC_INNER GC_bool GC_dirty_init(void)
-{
+  static GC_bool proc_dirty_open_files(void)
+  {
     char buf[40];
 
-    if (GC_bytes_allocd != 0 || GC_bytes_allocd_before_gc != 0) {
-      memset(GC_written_pages, 0xff, sizeof(page_hash_table));
-      GC_VERBOSE_LOG_PRINTF(
-                "Allocated %lu bytes: all pages may have been written\n",
-                (unsigned long)(GC_bytes_allocd + GC_bytes_allocd_before_gc));
-    }
-
     (void)snprintf(buf, sizeof(buf), "/proc/%ld/pagedata", (long)getpid());
     buf[sizeof(buf) - 1] = '\0';
     GC_proc_fd = open(buf, O_RDONLY);
-    if (GC_proc_fd < 0) {
+    if (-1 == GC_proc_fd) {
       WARN("/proc open failed; cannot enable GC incremental mode\n", 0);
       return FALSE;
     }
     if (syscall(SYS_fcntl, GC_proc_fd, F_SETFD, FD_CLOEXEC) == -1)
       WARN("Could not set FD_CLOEXEC for /proc\n", 0);
+    return TRUE;
+  }
+
+# ifdef CAN_HANDLE_FORK
+    GC_INNER void GC_dirty_update_child(void)
+    {
+      if (-1 == GC_proc_fd)
+        return; /* GC incremental mode is off */
+
+      close(GC_proc_fd);
+      if (!proc_dirty_open_files())
+        GC_incremental = FALSE; /* should be safe to turn it off */
+    }
+# endif /* CAN_HANDLE_FORK */
 
+GC_INNER GC_bool GC_dirty_init(void)
+{
+    if (GC_bytes_allocd != 0 || GC_bytes_allocd_before_gc != 0) {
+      memset(GC_written_pages, 0xff, sizeof(page_hash_table));
+      GC_VERBOSE_LOG_PRINTF(
+                "Allocated %lu bytes: all pages may have been written\n",
+                (unsigned long)(GC_bytes_allocd + GC_bytes_allocd_before_gc));
+    }
+    if (!proc_dirty_open_files())
+      return FALSE;
     GC_proc_buf = GC_scratch_alloc(GC_proc_buf_size);
     if (GC_proc_buf == NULL)
       ABORT("Insufficient space for /proc read");
diff --git a/pthread_support.c b/pthread_support.c
index 84d2d971..6153717a 100644
--- a/pthread_support.c
+++ b/pthread_support.c
@@ -1170,7 +1170,10 @@ static void fork_child_proc(void)
       /* Turn off parallel marking in the child, since we are probably  */
       /* just going to exec, and we would have to restart mark threads. */
         GC_parallel = FALSE;
-#   endif /* PARALLEL_MARK */
+#   endif
+#   ifndef GC_DISABLE_INCREMENTAL
+      GC_dirty_update_child();
+#   endif
     RESTORE_CANCEL(fork_cancel_state);
     UNLOCK();
     /* Even though after a fork the child only inherits the single      */