linux-kernel - Re: [PATCH 2/6] mm: introduce vma_set

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Message-ID: <20201009151418.GW5177@ziepe.ca>
Date:   Fri, 9 Oct 2020 12:14:18 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christian König <ckoenig.leichtzumerken@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, dri-devel@...ts.freedesktop.org,
        linux-media@...r.kernel.org, chris@...is-wilson.co.uk,
        airlied@...hat.com, akpm@...ux-foundation.org, daniel@...ll.ch,
        sumit.semwal@...aro.org, willy@...radead.org, jhubbard@...dia.com
Subject: Re: [PATCH 2/6] mm: introduce vma_set_file function v3

On Fri, Oct 09, 2020 at 05:03:38PM +0200, Christian König wrote:
> +/*
> + * Change backing file, only valid to use during initial VMA setup.
> + */
> +void vma_set_file(struct vm_area_struct *vma, struct file *file)
> +{
> +	if (file)
> +	        get_file(file);
> +
> +	swap(vma->vm_file, file);
> +
> +	if (file)
> +		fput(file);
> +}

fput crashes when file is NULL so the error handling after
unmap_and_free_vma: can't handle this case, similarly vm_file can't be
NULL either.

So just simply:

 swap(vma->vm_file, file);
 get_file(vma->vm_file);
 fput(file);
 
Will do?

Just let it crash if any of them are wrongly NULL.

Jason