From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steffen Klassert <steffen.klassert@secunet.com>
Subject: Re: [PATCH ipsec] xfrm: prevent ipcomp scratch buffer race condition
Date: Tue, 15 Oct 2013 11:46:03 +0200
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Cc: Michal Kubecek <mkubecek@suse.cz>,
	Herbert Xu <herbert@gondor.hengli.com.au>,
	"David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org
To: Fan Du <fan.du@windriver.com>
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On Tue, Oct 15, 2013 at 04:59:04PM +0800, Fan Du wrote:
>=20
>=20
> On 2013=E5=B9=B410=E6=9C=8815=E6=97=A5 16:33, Steffen Klassert wrote:
> >
> >Maybe we could disable the BHs before we fetch the percpu pointers.
> >Then we can use smp_processor_id() to get the cpu. With that we
> >could get rid of a (now useless) preempt_disable()/preempt_enable()
> >pair. Same could be done in ipcomp_compress().
>=20
> Is it possible that two tasks race scratch buffer when both of them t=
rying to compress data
> without preempt disabled? for example, when task A working on compres=
sion, then task B
> with higher priority preempts task A, and try to touch scratch buffer=
, which leaves stale
> data for task A after then.
>=20
> I think we needs preempt disabled for such case, otherwise I overlook=
 codes in somewhere else.
>=20

You overlook that preemption is disabled if the BHs are disabled.