Date:   Thu, 23 Feb 2023 15:28:44 -0500
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
        michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
        dave@stgolabs.net, willy@infradead.org, peterz@infradead.org,
        ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com,
        will@kernel.org, luto@kernel.org, songliubraving@fb.com,
        peterx@redhat.com, david@redhat.com, dhowells@redhat.com,
        hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev,
        punit.agrawal@bytedance.com, lstoakes@gmail.com,
        peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com,
        axelrasmussen@google.com, joelaf@google.com, minchan@google.com,
        rppt@kernel.org, jannh@google.com, shakeelb@google.com,
        tatashin@google.com, edumazet@google.com, gthelen@google.com,
        gurua@google.com, arjunroy@google.com, soheil@google.com,
        leewalsh@google.com, posk@google.com,
        michalechner92@googlemail.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or
 expanding it
Message-ID: <20230223202844.noant5suylne3dnh@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
        michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
        dave@stgolabs.net, willy@infradead.org, peterz@infradead.org,
        ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com,
        will@kernel.org, luto@kernel.org, songliubraving@fb.com,
        peterx@redhat.com, david@redhat.com, dhowells@redhat.com,
        hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev,
        punit.agrawal@bytedance.com, lstoakes@gmail.com,
        peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com,
        axelrasmussen@google.com, joelaf@google.com, minchan@google.com,
        rppt@kernel.org, jannh@google.com, shakeelb@google.com,
        tatashin@google.com, edumazet@google.com, gthelen@google.com,
        gurua@google.com, arjunroy@google.com, soheil@google.com,
        leewalsh@google.com, posk@google.com, michalechner92@googlemail.com,
        linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
References: <20230216051750.3125598-1-surenb@google.com>
 <20230216051750.3125598-18-surenb@google.com>
 <20230223202011.dahh6cidqxhzoxne@revolver>
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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@Oracle.com> [230223 15:20]:
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> 
> * Suren Baghdasaryan <surenb@google.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@google.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
> >