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

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Date:   Tue, 2 Feb 2021 17:55:50 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Liam Mark <lmark@...eaurora.org>, labbott@...hat.com,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <john.stultz@...aro.org>,
        Christian König <christian.koenig@....com>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Ørjan Eide <orjan.eide@....com>,
        Robin Murphy <robin.murphy@....com>,
        James Jones <jajones@...dia.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        linux-media <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <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 2, 2021 at 5:31 PM Minchan Kim <minchan@...nel.org> wrote:
>
> 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.
> >
> > Suggested-by: Christoph Hellwig <hch@...radead.org>
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  mm/memory.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index feff48e1465a..e503c9801cd9 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> >               return -EINVAL;
> >       if (!(vma->vm_flags & VM_MIXEDMAP)) {
> >               BUG_ON(mmap_read_trylock(vma->vm_mm));
>
> Better to replace above BUG_ON with WARN_ON_ONCE, too?

If nobody objects I'll do that in the next respin. Thanks!

>
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