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Date: Mon, 29 Feb 2016 19:10:19 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Alex Deucher <alexander.deucher@amd.com>,
        Alex Thorlton <athorlton@sgi.com>,
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        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 13/18] exec: make exec path waiting for mmap_sem killable
Message-ID: <20160229181018.GF3615@redhat.com>
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On 02/29, Michal Hocko wrote:
>
> On Mon 29-02-16 18:23:34, Oleg Nesterov wrote:
> > On 02/29, Michal Hocko wrote:
> > >
> > > @@ -267,7 +267,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
> > >  	if (!vma)
> > >  		return -ENOMEM;
> > >
> > > -	down_write(&mm->mmap_sem);
> > > +	if (down_write_killable(&mm->mmap_sem)) {
> > > +		err = -EINTR;
> > > +		goto err_free;
> > > +	}
> > >  	vma->vm_mm = mm;
> >
> > I won't argue, but this looks unnecessary. Nobody else can see this new mm,
> > down_write() can't block.
> >
> > In fact I think we can just remove down_write/up_write here. Except perhaps
> > there is lockdep_assert_held() somewhere in these paths.
>
> This is what I had initially but then I've noticed that mm_alloc() does
> mm_init(current)->init_new_context(current)

yes, and init_new_context() is arch dependant...

> code doesn't seem much harder to follow, the callers are already
> handling all error paths so I guess it would be better to simply move on
> this.

Yes, agreed, please forget.

Oleg.