Commit 5eed6f1dff87bfb5e545935def3843edf42800f2 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.
Fixes: 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting")
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
kernel/fork.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index d6c324b1b29e..9ee28dfe7c21 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
}
