linux-kernel - Re: [PATCH 3/8] mm, hugetlb: fix race in region tracking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Mon, 3 Feb 2014 16:18:21 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	iamjoonsoo.kim@....com, riel@...hat.com, mgorman@...e.de,
	mhocko@...e.cz, aneesh.kumar@...ux.vnet.ibm.com,
	kamezawa.hiroyu@...fujitsu.com, hughd@...gle.com,
	david@...son.dropbear.id.au, js1304@...il.com,
	liwanp@...ux.vnet.ibm.com, dhillf@...il.com, rientjes@...gle.com,
	aswin@...com, scott.norton@...com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] mm, hugetlb: fix race in region tracking

On Tue, 28 Jan 2014 17:19:38 -0800 Davidlohr Bueso <davidlohr@...com> wrote:

> On Tue, 2014-01-28 at 19:36 -0500, Naoya Horiguchi wrote:
> > On Mon, Jan 27, 2014 at 06:34:17PM -0800, Davidlohr Bueso wrote:
> [...]
> > > > If this retry is really essential for the fix, please comment the reason
> > > > both in patch description and inline comment. It's very important for
> > > > future code maintenance.
> > > 
> > > So we locate the corresponding region in the reserve map, and if we are
> > > below the current region, then we allocate a new one. Since we dropped
> > > the lock to allocate memory, we have to make sure that we still need the
> > > new region and that we don't race with the new status of the reservation
> > > map. This is the whole point of the retry, and I don't see it being
> > > suboptimal.
> > 
> > I'm afraid that you don't explain why you need drop the lock for memory
> > allocation. Are you saying that this unlocking comes from the difference
> > between rwsem and spin lock?
> 
> Because you cannot go to sleep while holding a spinlock, which is
> exactly what kmalloc(GFP_KERNEL) can do. We *might* get a way with it
> with GFP_ATOMIC, I dunno, but I certainly prefer this approach better.

yup.  You could do

	foo = kmalloc(size, GFP_NOWAIT);
	if (!foo) {
		spin_unlock(...);
		foo = kmalloc(size, GFP_KERNEL);
		if (!foo)
			...
		spin_lock(...);
	}

that avoids the lock/unlock once per allocation.  But it also increases
the lock's average hold times....

		
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/