Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <bb5e3ab8-9c47-7d01-cdaa-1b4231312f67@linux.ibm.com>
Date:   Tue, 6 Sep 2022 17:35:22 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0)
 Gecko/20100101 Thunderbird/102.2.0
Subject: Re: [RFC PATCH RESEND 10/28] mm/mmap: mark VMAs as locked in
 vma_adjust
Content-Language: fr
To:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de,
        dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com,
        peterz@infradead.org, laurent.dufour@fr.ibm.com,
        paulmck@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,
        rientjes@google.com, axelrasmussen@google.com, joelaf@google.com,
        minchan@google.com, kernel-team@android.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org
References: <20220901173516.702122-1-surenb@google.com>
 <20220901173516.702122-11-surenb@google.com>
From:   Laurent Dufour <ldufour@linux.ibm.com>
In-Reply-To: <20220901173516.702122-11-surenb@google.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> vma_adjust modifies a VMA and possibly its neighbors. Mark them as locked
> before making the modifications.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  mm/mmap.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f89c9b058105..ed58cf0689b2 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -710,6 +710,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
>  	long adjust_next = 0;
>  	int remove_next = 0;
>  
> +	vma_mark_locked(vma);
> +	if (next)
> +		vma_mark_locked(next);
> +

I was wondering if the VMAs insert and expand should be locked too.

For expand, I can't see any valid reason, but for insert, I'm puzzled.
I would think that it is better to lock the VMA to be inserted but I can't
really justify that.

It may be nice to detail why this is not need to lock insert and expand here.

>  	if (next && !insert) {
>  		struct vm_area_struct *exporter = NULL, *importer = NULL;
>  
> @@ -754,8 +758,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
>  			 * If next doesn't have anon_vma, import from vma after
>  			 * next, if the vma overlaps with it.
>  			 */
> -			if (remove_next == 2 && !next->anon_vma)
> +			if (remove_next == 2 && !next->anon_vma) {
>  				exporter = next->vm_next;
> +				if (exporter)
> +					vma_mark_locked(exporter);
> +			}
>  
>  		} else if (end > next->vm_start) {
>  			/*
> @@ -931,6 +938,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
>  			 * "vma->vm_next" gap must be updated.
>  			 */
>  			next = vma->vm_next;
> +			if (next)
> +				vma_mark_locked(next);
>  		} else {
>  			/*
>  			 * For the scope of the comment "next" and