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Date:   Wed, 12 Apr 2023 17:29:38 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Stefan Roesch <shr@devkernel.io>
Cc:     kernel-team@fb.com, linux-mm@kvack.org, riel@surriel.com,
        mhocko@suse.com, david@redhat.com, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org, akpm@linux-foundation.org,
        hannes@cmpxchg.org, Bagas Sanjaya <bagasdotme@gmail.com>
Subject: Re: [PATCH v6 1/3] mm: add new api to enable ksm per process
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On Wed, Apr 12, 2023 at 09:08:11AM -0700, Stefan Roesch wrote:
> 
> 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?

You said 'int err' which declares a new variable.  If you want it
reported, just use 'error = ksm_add_mm(me->mm);'.