From: Andrea Arcangeli Date: Fri, 28 Jun 2019 19:07:14 +0000 (-0700) Subject: fork,memcg: alloc_thread_stack_node needs to set tsk->stack X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=1bf4580e00a248a2c86269125390eb3648e1877c;p=openwrt%2Fstaging%2Fblogic.git 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. Link: http://lkml.kernel.org/r/20190619011450.28048-1-aarcange@redhat.com Fixes: 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting") Signed-off-by: Andrea Arcangeli Reviewed-by: Rik van Riel Acked-by: Roman Gushchin Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/fork.c b/kernel/fork.c index 399aca51ff75..61667909ce83 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -248,7 +248,11 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) 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 }