linux-kernel - Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

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Date:   Tue, 27 Mar 2018 16:31:23 +0200
From:   Mateusz Guzik <mguzik@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, adobriyan@...il.com,
        willy@...radead.org, gorcunov@...nvz.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct

On Tue, Mar 27, 2018 at 08:29:39AM +0200, Michal Hocko wrote:
> On Tue 27-03-18 02:20:39, Yang Shi wrote:
> [...]
> The patch looks reasonable to me. Maybe it would be better to be more
> explicit about the purpose of the patch. As others noticed, this alone
> wouldn't solve the mmap_sem contention issues. I _think_ that if you
> were more explicit about the mmap_sem abuse it would trigger less
> questions.
> 

>From what I gather even with other fixes the kernel will still end up
grabbing the semaphore. In this case I don't see what's the upside of
adding the spinlock for args. The downside is growth of mm_struct.

i.e. the code can be refactored to just hold the lock and relock only if
necessary (unable to copy to user without faulting)

-- 
Mateusz Guzik