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Date:   Thu, 18 Apr 2019 15:03:10 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Laurent Dufour <ldufour@linux.ibm.com>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Michal Koutny <mkoutny@suse.com>
Subject: Re: [PATCH] mm: use mm.arg_lock in get_cmdline()
Message-ID: <20190418130310.GJ6567@dhcp22.suse.cz>
References: <20190418125827.57479-1-ldufour@linux.ibm.com>
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Michal has posted the same patch few days ago http://lkml.kernel.org/r/20190417120347.15397-1-mkoutny@suse.com

On Thu 18-04-19 14:58:27, Laurent Dufour wrote:
> The commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end
> and env_start|end in mm_struct") introduce the spinlock arg_lock to protect
> the arg_* and env_* field of the mm_struct structure.
> 
> While reading the code, I found that this new spinlock was not used in
> get_cmdline() to protect access to these fields.
> 
> Fixing this even if there is no issue reported yet for this.
> 
> Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
> Cc: Yang Shi <yang.shi@linux.alibaba.com>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> ---
>  mm/util.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 05a464929b3e..789760c3028b 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
>  	if (!mm->arg_end)
>  		goto out_mm;	/* Shh! No looking before we're done */
>  
> -	down_read(&mm->mmap_sem);
> +	spin_lock(&mm->arg_lock);
>  	arg_start = mm->arg_start;
>  	arg_end = mm->arg_end;
>  	env_start = mm->env_start;
>  	env_end = mm->env_end;
> -	up_read(&mm->mmap_sem);
> +	spin_unlock(&mm->arg_lock);
>  
>  	len = arg_end - arg_start;
>  
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs