linux-kernel - Re: [PATCH] exit: clear TIF_MEMDIE after exit_task

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Message-ID: <20160314163943.GE11400@dhcp22.suse.cz>
Date:	Mon, 14 Mar 2016 17:39:43 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exit: clear TIF_MEMDIE after exit_task_work

On Tue 01-03-16 19:20:24, Michael S. Tsirkin wrote:
> On Tue, Mar 01, 2016 at 06:17:58PM +0100, Michal Hocko wrote:
[...]
> > Sorry, I could have been more verbose... The code would have to make sure
> > that the mm is still alive before calling g-u-p by
> > atomic_inc_not_zero(&mm->mm_users) and fail if the user count dropped to
> > 0 in the mean time. See how fs/proc/task_mmu.c does that (proc_mem_open
> > + m_start + m_stop.
> > 
> > The biggest advanatage would be that the mm address space pin would be
> > only for the particular operation. Not sure whether that is possible in
> > the driver though. Anyway pinning the mm for a potentially unbounded
> > amount of time doesn't sound too nice.
> 
> Hmm that would be another atomic on data path ...
> I'd have to explore that.

Did you have any chance to look into this?
-- 
Michal Hocko
SUSE Labs