linux-kernel - Re: [PATCH] mm: use mm.arg_lock in get

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Date:   Thu, 18 Apr 2019 09:48:09 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Koutny <mkoutny@...e.com>
Subject: Re: [PATCH] mm: use mm.arg_lock in get_cmdline()



On 4/18/19 6:05 AM, Laurent Dufour wrote:
> 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.

Yes, Michal already posted a similar patch. Anyway, thanks for catching 
this.

>
>> 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@...ux.alibaba.com>
>>> Signed-off-by: Laurent Dufour <ldufour@...ux.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
>>