linux-kernel - Re: [PATCH -mm v3] mm/page_isolation: fix potential warning from user

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Message-ID: <20200120171659.GA29276@dhcp22.suse.cz>
Date:   Mon, 20 Jan 2020 18:16:59 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, david@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v3] mm/page_isolation: fix potential warning from user

On Mon 20-01-20 11:39:15, Qian Cai wrote:
> It makes sense to call the WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE)
> from start_isolate_page_range(), but should avoid triggering it from
> userspace, i.e, from is_mem_section_removable() because it could crash
> the system by a non-root user if warn_on_panic is set.
> 
> While at it, simplify the code a bit by removing an unnecessary jump
> label.
> 
> Suggested-by: Michal Hocko <mhocko@...nel.org>
> Signed-off-by: Qian Cai <cai@....pw>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
> 
> v3: Drop the page_isolation.c cleanup change.
> v2: Improve the commit log.
>     Warn for all start_isolate_page_range() users not just offlining.
> 
>  mm/page_alloc.c     | 11 ++++-------
>  mm/page_isolation.c | 18 +++++++++++-------
>  2 files changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 621716a25639..3c4eb750a199 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8231,7 +8231,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		if (is_migrate_cma(migratetype))
>  			return NULL;
>  
> -		goto unmovable;
> +		return page;
>  	}
>  
>  	for (; iter < pageblock_nr_pages; iter++) {
> @@ -8241,7 +8241,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		page = pfn_to_page(pfn + iter);
>  
>  		if (PageReserved(page))
> -			goto unmovable;
> +			return page;
>  
>  		/*
>  		 * If the zone is movable and we have ruled out all reserved
> @@ -8261,7 +8261,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  			unsigned int skip_pages;
>  
>  			if (!hugepage_migration_supported(page_hstate(head)))
> -				goto unmovable;
> +				return page;
>  
>  			skip_pages = compound_nr(head) - (page - head);
>  			iter += skip_pages - 1;
> @@ -8303,12 +8303,9 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>  		 * is set to both of a memory hole page and a _used_ kernel
>  		 * page at boot.
>  		 */
> -		goto unmovable;
> +		return page;
>  	}
>  	return NULL;
> -unmovable:
> -	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> -	return pfn_to_page(pfn + iter);
>  }
>  
>  #ifdef CONFIG_CONTIG_ALLOC
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index e70586523ca3..a9fd7c740c23 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -54,14 +54,18 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>  
>  out:
>  	spin_unlock_irqrestore(&zone->lock, flags);
> -	if (!ret)
> +	if (!ret) {
>  		drain_all_pages(zone);
> -	else if ((isol_flags & REPORT_FAILURE) && unmovable)
> -		/*
> -		 * printk() with zone->lock held will guarantee to trigger a
> -		 * lockdep splat, so defer it here.
> -		 */
> -		dump_page(unmovable, "unmovable page");
> +	} else {
> +		WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> +
> +		if ((isol_flags & REPORT_FAILURE) && unmovable)
> +			/*
> +			 * printk() with zone->lock held will likely trigger a
> +			 * lockdep splat, so defer it here.
> +			 */
> +			dump_page(unmovable, "unmovable page");
> +	}
>  
>  	return ret;
>  }
> -- 
> 2.21.0 (Apple Git-122.2)

-- 
Michal Hocko
SUSE Labs