linux-kernel - Re: [PATCH v2 6/6] fs/proc/kcore: use page_offline

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Date:   Mon, 17 May 2021 09:44:21 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Steven Price <steven.price@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Aili Yao <yaoaili@...gsoft.com>, Jiri Bohac <jbohac@...e.cz>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 6/6] fs/proc/kcore: use page_offline_(freeze|thaw)

On Fri, May 14, 2021 at 07:22:47PM +0200, David Hildenbrand wrote:
> Let's properly synchronize with drivers that set PageOffline().
> Unfreeze/thaw every now and then, so drivers that want to set PageOffline()
> can make progress.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Acked-by: Mike Rapoport <rppt@...ux.ibm.com>

> ---
>  fs/proc/kcore.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 92ff1e4436cb..982e694aae77 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -313,6 +313,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  {
>  	char *buf = file->private_data;
>  	size_t phdrs_offset, notes_offset, data_offset;
> +	size_t page_offline_frozen = 1;
>  	size_t phdrs_len, notes_len;
>  	struct kcore_list *m;
>  	size_t tsz;
> @@ -322,6 +323,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  	int ret = 0;
>  
>  	down_read(&kclist_lock);
> +	/*
> +	 * Don't race against drivers that set PageOffline() and expect no
> +	 * further page access.
> +	 */
> +	page_offline_freeze();
>  
>  	get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
>  	phdrs_offset = sizeof(struct elfhdr);
> @@ -480,6 +486,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  			}
>  		}
>  
> +		if (page_offline_frozen++ % MAX_ORDER_NR_PAGES == 0) {
> +			page_offline_thaw();
> +			cond_resched();
> +			page_offline_freeze();
> +		}
> +
>  		if (&m->list == &kclist_head) {
>  			if (clear_user(buffer, tsz)) {
>  				ret = -EFAULT;
> @@ -565,6 +577,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  	}
>  
>  out:
> +	page_offline_thaw();
>  	up_read(&kclist_lock);
>  	if (ret)
>  		return ret;
> -- 
> 2.31.1
> 

-- 
Sincerely yours,
Mike.