netdev - Re: [PATCH v2] xfrm: policy: Read seqcount outside of rcu-read side in xfrm_policy_lookup

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Date:   Thu, 3 Jun 2021 10:16:43 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
CC:     Varad Gautam <varad.gautam@...e.com>,
        <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        <netdev@...r.kernel.org>, <stable@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Florian Westphal" <fw@...len.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH v2] xfrm: policy: Read seqcount outside of rcu-read side
 in xfrm_policy_lookup_bytype

On Fri, May 28, 2021 at 06:44:37PM +0200, Ahmed S. Darwish wrote:
> On Fri, May 28, 2021, Varad Gautam wrote:
> >
> > Thead 1 (xfrm_hash_resize)	Thread 2 (xfrm_policy_lookup_bytype)
> >
> > 				rcu_read_lock();
> > mutex_lock(&hash_resize_mutex);
> > 				read_seqcount_begin(&xfrm_policy_hash_generation);
> > 				mutex_lock(&hash_resize_mutex); // block
> > xfrm_bydst_resize();
> > synchronize_rcu(); // block
> > 		<RCU stalls in xfrm_policy_lookup_bytype>
> >
> ...
> >
> > Fixes: 77cc278f7b20 ("xfrm: policy: Use sequence counters with associated lock")
> > Signed-off-by: Varad Gautam <varad.gautam@...e.com>
> 
> Acked-by: Ahmed S. Darwish <a.darwish@...utronix.de>

Applied, thanks a lot!