linux-kernel - Re: [PATCH 13/18] exec: make exec path waiting for mmap

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Message-ID: <20160229181018.GF3615@redhat.com>
Date:	Mon, 29 Feb 2016 19:10:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alex Deucher <alexander.deucher@....com>,
	Alex Thorlton <athorlton@....com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Christian König <christian.koenig@....com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-arch@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Cermak <petrcermak@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 13/18] exec: make exec path waiting for mmap_sem killable

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.