Matthew Wilcox willy@infradead.org writes:

On Tue, Apr 11, 2023 at 08:16:46PM -0700, Stefan Roesch wrote:

...

case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; +#ifdef CONFIG_KSM

• case PR_SET_MEMORY_MERGE:

• if (mmap_write_lock_killable(me->mm))
  

• 	return -EINTR;
  

• if (arg2) {
  

• 	int err = ksm_add_mm(me->mm);
  

• 	if (!err)
  

• 		ksm_add_vmas(me->mm);
  

in the last version of this patch, you reported the error. Now you swallow the error. I have no idea which is correct, but you've changed the behaviour without explaining it, so I assume it's wrong.

I don't see how the error is swallowed in the arg2 case. If there is an error ksm_add_vmas is not executedd and at the end of the function the error is returned. Am I missing something?

...

• } else {
  

• 	clear_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
  

• }
  

• mmap_write_unlock(me->mm);
  

• break;
  

• case PR_GET_MEMORY_MERGE:

• if (arg2 || arg3 || arg4 || arg5)
  

• 	return -EINVAL;
  

• error = !!test_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
  

• break;
  

Why do we need a GET? Just for symmetry, or is there an actual need for it?

There are three reasons: - For symmetry - The ksm sharing is inherited by child processes. This allows the test programs to verify that this is working. - For child processes it might be useful to have the ability to check if ksm sharing has been enabled