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Subject: Re: [PATCH] mm: use mm.arg_lock in get_cmdline()
To:     Michal Hocko <mhocko@kernel.org>
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>
References: <20190418125827.57479-1-ldufour@linux.ibm.com>
 <20190418130310.GJ6567@dhcp22.suse.cz>
From:   Laurent Dufour <ldufour@linux.ibm.com>
Date:   Thu, 18 Apr 2019 15:05:21 +0200
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Le 18/04/2019 à 15:03, Michal Hocko a écrit :
> Michal has posted the same patch few days ago http://lkml.kernel.org/r/20190417120347.15397-1-mkoutny@suse.com

Oups, sorry for the noise, I missed it.

> 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
>