Date:   Thu, 23 Feb 2023 15:20:11 -0500
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     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: <20230223202011.dahh6cidqxhzoxne@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
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        gurua@google.com, arjunroy@google.com, soheil@google.com,
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        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
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References: <20230216051750.3125598-1-surenb@google.com>
 <20230216051750.3125598-18-surenb@google.com>
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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
>