fork,memcg: alloc_thread_stack_node needs to set tsk->stack

Commit 5eed6f1dff87 ("fork,memcg: fix crash in free_thread_stack on memcg charge fail") corrected two instances, but there was a third instance of this bug. Without setting tsk->stack, if memcg_charge_kernel_stack fails, it'll execute free_thread_stack() on a dangling pointer. Enterprise kernels are compiled with VMAP_STACK=y so this isn't critical, but custom VMAP_STACK=n builds should have some performance advantage, with the drawback of risking to fail fork because compaction didn't succeed. So as long as VMAP_STACK=n is a supported option it's worth fixing it upstream.

Andrea Arcangeli committed 7 years ago

Commit 1bf45801 parent 8708e131 file · +5 −1Browse files

Unified · Split

kernel/fork.c+5−1

 	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
 					     THREAD_SIZE_ORDER);
-	return page ? page_address(page) : NULL;
+	if (likely(page)) {
+		tsk->stack = page_address(page);
+		return tsk->stack;
+	}
+	return NULL;
 #endif
 }