Unmap MAP_SHARED stacks on fork()

Author: riptl

src/disco/topo/fd_topo_run.c

@@ -197,6 +197,11 @@ fd_topo_tile_stack_join( char const * app_name,
                          MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, (off_t)0 )!=guard_hi ) )
     FD_LOG_ERR(( "mmap failed (%i-%s)", errno, fd_io_strerror( errno ) ));
 
+  /* fork() is incompatible with MAP_SHARED */
+  if( FD_UNLIKELY( madvise( stack, FD_TILE_PRIVATE_STACK_SZ, MADV_DONTFORK ) ) ) {
+    FD_LOG_ERR(( "madvise(stack,MADV_DONTFORK) failed (%i-%s)", errno, fd_io_strerror( errno ) ));
+  }
+
   return stack;
 }
 

src/util/tile/fd_tile_threads.cxx

@@ -160,6 +160,12 @@ fd_tile_private_stack_new( int   optimize,
     FD_LOG_WARNING(( "fd_tile: mmap failed (%i-%s)\n\tAttempting to continue without stack guard hi.",
                      errno, fd_io_strerror( errno ) ));
 
+  /* Prevent fork() from smashing the stack */
+
+  if( FD_UNLIKELY( madvise( stack, FD_TILE_PRIVATE_STACK_SZ, MADV_DONTFORK ) ) ) {
+    FD_LOG_ERR(( "madvise(stack,MADV_DONTFORK) failed (%i-%s)", errno, fd_io_strerror( errno ) ));
+  }
+
   return stack;
 }