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

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Date:   Fri, 28 May 2021 18:44:37 +0200
From:   "Ahmed S. Darwish" <a.darwish@...utronix.de>
To:     Varad Gautam <varad.gautam@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        netdev@...r.kernel.org, stable@...r.kernel.org,
        Steffen Klassert <steffen.klassert@...unet.com>,
        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, 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>