From: Andrea Arcangeli aarcange@redhat.com
[ Upstream commit 1bf4580e00a248a2c86269125390eb3648e1877c ]
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 aarcange@redhat.com Reviewed-by: Rik van Riel riel@surriel.com Acked-by: Roman Gushchin guro@fb.com Acked-by: Michal Hocko mhocko@suse.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/fork.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 1bd119530a49..1a2d18e98bf9 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -240,7 +240,11 @@ 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 }