Re: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed

[Oleg Nesterov]

On 07/25, Song Liu wrote:
>
> I guess I know the case now. We can probably avoid this with an simple 
> check for old_page == new_page?

better yet, I think we can check PageAnon(old_page) and avoid the unnecessary
__replace_page() in this case. See the patch below.

Anyway, why __replace_page() needs to lock both pages? This doesn't look nice
even if it were correct. I think it can do lock_page(old_page) later.

Oleg.


--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -488,6 +488,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, 
struct mm_struct *mm,
                ref_ctr_updated = 1;
        }
 
+       ret = 0;
+       if (!is_register && !PageAnon(old_page))
+               goto put_old;
+
        ret = anon_vma_prepare(vma);
        if (ret)
                goto put_old;