mld: get rid of inet6_dev->mc_lock

The purpose of mc_lock is to protect inet6_dev->mc_tomb.
But mc_tomb is already protected by RTNL and all functions,
which manipulate mc_tomb are called under RTNL.
So, mc_lock is not needed.
Furthermore, it is spinlock so the critical section is atomic.
In order to reduce atomic context, it should be removed.

Suggested-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/if_inet6.h

@@ -167,7 +167,6 @@ struct inet6_dev {
 
 	struct ifmcaddr6	*mc_list;
 	struct ifmcaddr6	*mc_tomb;
-	spinlock_t		mc_lock;
 
 	unsigned char		mc_qrv;		/* Query Robustness Variable */
 	unsigned char		mc_gq_running;

net/ipv6/mcast.c

@@ -752,10 +752,8 @@ static void mld_add_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
 	}
 	spin_unlock_bh(&im->mca_lock);
 
-	spin_lock_bh(&idev->mc_lock);
 	pmc->next = idev->mc_tomb;
 	idev->mc_tomb = pmc;
-	spin_unlock_bh(&idev->mc_lock);
 }
 
 static void mld_del_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
@@ -764,7 +762,6 @@ static void mld_del_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
 	struct ip6_sf_list *psf;
 	struct in6_addr *pmca = &im->mca_addr;
 
-	spin_lock_bh(&idev->mc_lock);
 	pmc_prev = NULL;
 	for (pmc = idev->mc_tomb; pmc; pmc = pmc->next) {
 		if (ipv6_addr_equal(&pmc->mca_addr, pmca))
@@ -777,7 +774,6 @@ static void mld_del_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
 		else
 			idev->mc_tomb = pmc->next;
 	}
-	spin_unlock_bh(&idev->mc_lock);
 
 	spin_lock_bh(&im->mca_lock);
 	if (pmc) {
@@ -801,10 +797,8 @@ static void mld_clear_delrec(struct inet6_dev *idev)
 {
 	struct ifmcaddr6 *pmc, *nextpmc;
 
-	spin_lock_bh(&idev->mc_lock);
 	pmc = idev->mc_tomb;
 	idev->mc_tomb = NULL;
-	spin_unlock_bh(&idev->mc_lock);
 
 	for (; pmc; pmc = nextpmc) {
 		nextpmc = pmc->next;
@@ -1907,7 +1901,6 @@ static void mld_send_cr(struct inet6_dev *idev)
 	int type, dtype;
 
 	read_lock_bh(&idev->lock);
-	spin_lock(&idev->mc_lock);
 
 	/* deleted MCA's */
 	pmc_prev = NULL;
@@ -1941,7 +1934,6 @@ static void mld_send_cr(struct inet6_dev *idev)
 		} else
 			pmc_prev = pmc;
 	}
-	spin_unlock(&idev->mc_lock);
 
 	/* change recs */
 	for (pmc = idev->mc_list; pmc; pmc = pmc->next) {
@@ -2582,7 +2574,6 @@ void ipv6_mc_up(struct inet6_dev *idev)
 void ipv6_mc_init_dev(struct inet6_dev *idev)
 {
 	write_lock_bh(&idev->lock);
-	spin_lock_init(&idev->mc_lock);
 	idev->mc_gq_running = 0;
 	INIT_DELAYED_WORK(&idev->mc_gq_work, mld_gq_work);
 	idev->mc_tomb = NULL;