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Date: Mon, 29 Feb 2016 19:10:19 +0100
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 13/18] exec: make exec path waiting for mmap_sem killable
Message-ID: <20160229181018.GF3615@redhat.com>
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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>, Andrea Arcangeli <aarcange@redhat.com>, Andy Lutomirski <luto@amacapital.net>, Benjamin LaHaise <bcrl@kvack.org>, Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, Daniel Vetter <daniel.vetter@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, David Airlie <airlied@linux.ie>, Davidlohr Bueso <dave@stgolabs.net>, David Rientjes <rientjes@google.com>, "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Konstantin Khlebnikov <koct9i@gmail.com>, linux-arch@vger.kernel.org, Mel Gorman <mgorman@suse.de>, Peter Zijlstra <peterz@infradead.org>, Petr Cermak <petrcermak@chromium.org>, Thomas Gleixner <tglx@linutronix.de>, Alexander Viro <viro@zeniv.linux.org.uk>

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.

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