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Subject: Re: [PATCH] xfrm: policy: Read seqcount outside of rcu-read side in
 xfrm_policy_lookup_bytype
To:     "Ahmed S. Darwish" <a.darwish@linutronix.de>
CC:     linux-kernel@vger.kernel.org,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        netdev@vger.kernel.org, stable@vger.kernel.org,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Florian Westphal <fw@strlen.de>
References: <20210528120357.29542-1-varad.gautam@suse.com>
 <YLEIEa6DLjgd5mu5@lx-t490>
From:   Varad Gautam <varad.gautam@suse.com>
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Date:   Fri, 28 May 2021 18:06:07 +0200
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On 5/28/21 5:11 PM, 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: a7c44247f70 ("xfrm: policy: make xfrm_policy_lookup_bytype lockle=
ss")
>=20
> Minor note: the 'Fixes' commit should be 77cc278f7b20 ("xfrm: policy:
> Use sequence counters with associated lock") instead.
>=20
> The reason read_seqcount_begin() is emitting a mutex_lock() on
> PREEMPT_RT is because of the s/seqcount_t/seqcount_mutex_t/ change.
>=20

Thanks, corrected it in v2.

> Kind regards,
>=20
> --
> Ahmed S. Darwish
> Linutronix GmbH
>=20

--=20
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