linux-kernel - Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or expanding it

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Message-ID: <20230223202844.noant5suylne3dnh@revolver>
Date:   Thu, 23 Feb 2023 15:28:44 -0500
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org,
        michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
        dave@...olabs.net, willy@...radead.org, peterz@...radead.org,
        ldufour@...ux.ibm.com, paulmck@...nel.org, mingo@...hat.com,
        will@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        punit.agrawal@...edance.com, lstoakes@...il.com,
        peterjung1337@...il.com, rientjes@...gle.com, chriscli@...gle.com,
        axelrasmussen@...gle.com, joelaf@...gle.com, minchan@...gle.com,
        rppt@...nel.org, jannh@...gle.com, shakeelb@...gle.com,
        tatashin@...gle.com, edumazet@...gle.com, gthelen@...gle.com,
        gurua@...gle.com, arjunroy@...gle.com, soheil@...gle.com,
        leewalsh@...gle.com, posk@...gle.com,
        michalechner92@...glemail.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or
 expanding it


Wait, I figured a better place to do this.

init_multi_vma_prep() should vma_start_write() on any VMA that is passed
in.. that we we catch any modifications here & in vma_merge(), which I
think is missed in this patch set?


* Liam R. Howlett <Liam.Howlett@...cle.com> [230223 15:20]:
> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> 
> * Suren Baghdasaryan <surenb@...gle.com> [230216 00:18]:
> > vma_expand and vma_shrink change VMA boundaries. Expansion might also
> > result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent
> > concurrent page faults.
> > 
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  mm/mmap.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index ec2f8d0af280..f079e5bbcd57 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  		ret = dup_anon_vma(vma, next);
> >  		if (ret)
> >  			return ret;
> > +
> > +		/* Lock the VMA  before removing it */
> > +		vma_start_write(next);
> >  	}
> >  
> >  	init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
> > @@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  	if (vma_iter_prealloc(vmi))
> >  		goto nomem;
> >  
> > +	vma_start_write(vma);
> >  	vma_adjust_trans_huge(vma, start, end, 0);
> >  	/* VMA iterator points to previous, so set to start if necessary */
> >  	if (vma_iter_addr(vmi) != start)
> > @@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  	if (vma_iter_prealloc(vmi))
> >  		return -ENOMEM;
> >  
> > +	vma_start_write(vma);
> >  	init_vma_prep(&vp, vma);
> >  	vma_adjust_trans_huge(vma, start, end, 0);
> >  	vma_prepare(&vp);
> > -- 
> > 2.39.1
> >