linux-kernel - Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

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Message-ID: <097488c7-ab18-367b-c435-7c26d149c619@linux.alibaba.com>
Date:   Tue, 10 Apr 2018 09:21:19 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     adobriyan@...il.com, willy@...radead.org, mguzik@...hat.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct



On 4/10/18 5:28 AM, Cyrill Gorcunov wrote:
> On Tue, Apr 10, 2018 at 01:10:01PM +0200, Michal Hocko wrote:
>>> Because do_brk does vma manipulations, for this reason it's
>>> running under down_write_killable(&mm->mmap_sem). Or you
>>> mean something else?
>> Yes, all we need the new lock for is to get a consistent view on brk
>> values. I am simply asking whether there is something fundamentally
>> wrong by doing the update inside the new lock while keeping the original
>> mmap_sem locking in the brk path. That would allow us to drop the
>> mmap_sem lock in the proc path when looking at brk values.
> Michal gimme some time. I guess  we might do so, but I need some
> spare time to take more precise look into the code, hopefully today
> evening. Also I've a suspicion that we've wracked check_data_rlimit
> with this new lock in prctl. Need to verify it again.

I see you guys points. We might be able to move the drop of mmap_sem 
before setting mm->brk in sys_brk since mmap_sem should be used to 
protect vma manipulation only, then protect the value modify with the 
new arg_lock. Then we can eliminate mmap_sem stuff in prctl path, and it 
also prevents from wrecking check_data_rlimit.

At the first glance, it looks feasible to me. Will look into deeper later.

Thanks,
Yang