linux-kernel - Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert

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Date:   Wed, 3 Feb 2021 01:55:53 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     sumit.semwal@...aro.org, akpm@...ux-foundation.org,
        hch@...radead.org, lmark@...eaurora.org, labbott@...hat.com,
        Brian.Starkey@....com, john.stultz@...aro.org,
        christian.koenig@....com, cgoldswo@...eaurora.org,
        orjan.eide@....com, robin.murphy@....com, jajones@...dia.com,
        minchan@...nel.org, hridya@...gle.com, sspatil@...gle.com,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return
 of an error

On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> WARN_ON_ONCE and returning an error. This is to ensure users of the
> vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> and get an indication of an error without panicing the kernel.
> This will help identifying drivers that need to clear VM_PFNMAP before
> using dmabuf system heap which is moving to use vm_insert_page.

NACK.

The system may not _panic_, but it is clearly now _broken_.  The device
doesn't work, and so the system is useless.  You haven't really improved
anything here.  Just bloated the kernel with yet another _ONCE variable
that in a normal system will never ever ever be triggered.