linux-kernel - Re: [PATCH] mm, memory_hotplug: __offline

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Date:   Tue, 15 Jan 2019 18:02:13 +0100
From:   Jan Kara <jack@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
        Oscar Salvador <OSalvador@...e.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, memory_hotplug: __offline_pages fix wrong locking

On Tue 15-01-19 13:03:07, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> Jan has noticed that we do double unlock on some failure paths when
> offlining a page range. This is indeed the case when test_pages_in_a_zone
> respp. start_isolate_page_range fail. This was an omission when forward
> porting the debugging patch from an older kernel.
> 
> Fix the issue by dropping mem_hotplug_done from the failure condition
> and keeping the single unlock in the catch all failure path.
> 
> Reported-by: Jan Kara <jack@...e.cz>
> Fixes: 7960509329c2 ("mm, memory_hotplug: print reason for the offlining failure")
> Signed-off-by: Michal Hocko <mhocko@...e.com>

The patch looks good to me so feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

Also it fixes the test that previously crashed for me so you can add:

Tested-by: Jan Kara <jack@...e.cz>

								Honza


> ---
>  mm/memory_hotplug.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b9a667d36c55..faeeaccc5fae 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1576,7 +1576,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	   we assume this for now. .*/
>  	if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start,
>  				  &valid_end)) {
> -		mem_hotplug_done();
>  		ret = -EINVAL;
>  		reason = "multizone range";
>  		goto failed_removal;
> @@ -1591,7 +1590,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  				       MIGRATE_MOVABLE,
>  				       SKIP_HWPOISON | REPORT_FAILURE);
>  	if (ret) {
> -		mem_hotplug_done();
>  		reason = "failure to isolate range";
>  		goto failed_removal;
>  	}
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR