netdev - Re: [PATCH v1 net-next 02/15] ipv6: mcast: Replace locking comments with lockdep annotations.

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Message-ID: <20250619181152.1621004-1-kuni1840@gmail.com>
Date: Thu, 19 Jun 2025 11:11:44 -0700
From: Kuniyuki Iwashima <kuni1840@...il.com>
To: pabeni@...hat.com
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	horms@...nel.org,
	kuba@...nel.org,
	kuni1840@...il.com,
	kuniyu@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 02/15] ipv6: mcast: Replace locking comments with lockdep annotations.

From: Paolo Abeni <pabeni@...hat.com>
Date: Thu, 19 Jun 2025 13:56:26 +0200
> On 6/17/25 1:28 AM, Kuniyuki Iwashima wrote:
> > @@ -2072,10 +2086,7 @@ static void mld_send_report(struct inet6_dev *idev, struct ifmcaddr6 *pmc)
> >  		mld_sendpack(skb);
> >  }
> >  
> > -/*
> > - * remove zero-count source records from a source filter list
> > - * called with mc_lock
> > - */
> > +/* remove zero-count source records from a source filter list */
> >  static void mld_clear_zeros(struct ip6_sf_list __rcu **ppsf, struct inet6_dev *idev)
> >  {
> >  	struct ip6_sf_list *psf_prev, *psf_next, *psf;
> > @@ -2099,7 +2110,6 @@ static void mld_clear_zeros(struct ip6_sf_list __rcu **ppsf, struct inet6_dev *i
> >  	}
> >  }
> >  
> > -/* called with mc_lock */
> >  static void mld_send_cr(struct inet6_dev *idev)
> >  {
> >  	struct ifmcaddr6 *pmc, *pmc_prev, *pmc_next;
> 
> Why are you not adding the annotation in the above 2 places? AFAICS
> mld_send_cr() is called only by mld_ifc_work(), after acquiring the
> relevant lock, and mld_clear_zeros() is only called by mld_send_cr(),
> still under the same lock.

The two functions use mc_dereference() at the entrance,

static void mld_clear_zeros(struct ip6_sf_list __rcu **ppsf, struct inet6_dev *idev)
{
	struct ip6_sf_list *psf_prev, *psf_next, *psf;

	psf_prev = NULL;
	for (psf = mc_dereference(*ppsf, idev);

and I thought it would be redundant like

	ASSERT_RTNL();

	ptr = rtnl_dereference()