linux-kernel - Re: introduce probe_slab

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Message-Id: <20141022.145950.1585224138048242923.davem@davemloft.net>
Date:	Wed, 22 Oct 2014 14:59:50 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	oleg@...hat.com
Cc:	peterz@...radead.org, cl@...ux.com, tkhai@...dex.ru,
	ktkhai@...allels.com, linux-kernel@...r.kernel.org,
	mingo@...hat.com, vdavydov@...allels.com
Subject: Re: introduce probe_slab_address?

From: Oleg Nesterov <oleg@...hat.com>
Date: Wed, 22 Oct 2014 20:14:12 +0200

> So perhaps something like this makes sense?
> 
> If some arch has problems with D-cache aliasing (because the freed page
> can be already mapped by user-space or vmalloc'ed), it can redefine this
> helper.
> 
> Do you think we can use it to access rq->curr? (although let me repeat
> that I won't really argue with SLAB_DESTROY_BY_RCU).

Do we really need this?

We fully initialize and read from the area using the same virtual
address, there is no possiblity for corruption from SLAB's
perspective.

It's when you store at vaddr X then read at vaddr Y and expect to see
what you wrote at X that you have problems.

That is very much not what is happening here.

The lifetime is contained to SLAB's usage at one single virtual
address.
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