linux-kernel - Re: [PATCH v3 08/13] mm: add ability to take further action in vm_area

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Message-ID: <1b013d8d-47c8-4a74-8d7b-4cd8d3b8f2e2@lucifer.local>
Date: Tue, 16 Sep 2025 20:31:52 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>,
        Guo Ren <guoren@...nel.org>,
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Subject: Re: [PATCH v3 08/13] mm: add ability to take further action in
 vm_area_desc

On Tue, Sep 16, 2025 at 03:08:54PM -0300, Jason Gunthorpe wrote:
> On Tue, Sep 16, 2025 at 06:57:56PM +0100, Lorenzo Stoakes wrote:
> > > > +	/*
> > > > +	 * If an error occurs, unmap the VMA altogether and return an error. We
> > > > +	 * only clear the newly allocated VMA, since this function is only
> > > > +	 * invoked if we do NOT merge, so we only clean up the VMA we created.
> > > > +	 */
> > > > +	if (err) {
> > > > +		const size_t len = vma_pages(vma) << PAGE_SHIFT;
> > > > +
> > > > +		do_munmap(current->mm, vma->vm_start, len, NULL);
> > > > +
> > > > +		if (action->error_hook) {
> > > > +			/* We may want to filter the error. */
> > > > +			err = action->error_hook(err);
> > > > +
> > > > +			/* The caller should not clear the error. */
> > > > +			VM_WARN_ON_ONCE(!err);
> > > > +		}
> > > > +		return err;
> > > > +	}
> > > Also seems like this cleanup wants to be in a function that is not
> > > protected by #ifdef nommu since the code is identical on both branches.
> >
> > Not sure which cleanup you mean, this is new code :)
>
> I mean the code I quoted right abouve that cleans up the VMA on
> error.. It is always the same finishing sequence, there is no nommu
> dependency in it.

Ah right yeah.

I wonder if it's useful if err != 0 for nommu anyway.

>
> Just put it all in some "finish mmap complete" function and call it in
> both mmu and nommu versions.

Ack!

>
> Jason
>

Cheers, Lorenzo