mld: convert ip6_sf_list to RCU

The ip6_sf_list has been protected by mca_lock(spin_lock) so that the
critical section is atomic context. In order to switch this context,
changing locking is needed. The ip6_sf_list actually already protected
by RTNL So if it's converted to use RCU, its control path context can
be switched to sleepable.
But It doesn't remove mca_lock yet because ifmcaddr6 isn't converted
to RCU yet. So, It's not fully converted to the sleepable context.

Suggested-by: Cong Wang <[e-mail]>
Signed-off-by: Taehee Yoo <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/if_inet6.h

···
 };
 
 struct ip6_sf_list {
-	struct ip6_sf_list	*sf_next;
+	struct ip6_sf_list __rcu *sf_next;
 	struct in6_addr		sf_addr;
 	unsigned long		sf_count[2];	/* include/exclude counts */
 	unsigned char		sf_gsresp;	/* include in g & s response? */
 	unsigned char		sf_oldin;	/* change state */
 	unsigned char		sf_crcount;	/* retrans. left to send */
+	struct rcu_head		rcu;
 };
 
 #define MAF_TIMER_RUNNING	0x01
···
 	struct in6_addr		mca_addr;
 	struct inet6_dev	*idev;
 	struct ifmcaddr6	*next;
-	struct ip6_sf_list	*mca_sources;
-	struct ip6_sf_list	*mca_tomb;
+	struct ip6_sf_list	__rcu *mca_sources;
+	struct ip6_sf_list	__rcu *mca_tomb;
 	unsigned int		mca_sfmode;
 	unsigned char		mca_crcount;
 	unsigned long		mca_sfcount[2];

net/ipv6/mcast.c

···
  */
 
 #define for_each_pmc_rcu(np, pmc)				\
-	for (pmc = rcu_dereference(np->ipv6_mc_list);		\
-	     pmc != NULL;					\
+	for (pmc = rcu_dereference((np)->ipv6_mc_list);		\
+	     pmc;						\
 	     pmc = rcu_dereference(pmc->next))
+
+#define for_each_psf_rtnl(mc, psf)				\
+	for (psf = rtnl_dereference((mc)->mca_sources);		\
+	     psf;						\
+	     psf = rtnl_dereference(psf->sf_next))
+
+#define for_each_psf_rcu(mc, psf)				\
+	for (psf = rcu_dereference((mc)->mca_sources);		\
+	     psf;						\
+	     psf = rcu_dereference(psf->sf_next))
+
+#define for_each_psf_tomb(mc, psf)				\
+	for (psf = rtnl_dereference((mc)->mca_tomb);		\
+	     psf;						\
+	     psf = rtnl_dereference(psf->sf_next))
 
 static int unsolicited_report_interval(struct inet6_dev *idev)
 {
···
 	if (pmc->mca_sfmode == MCAST_INCLUDE) {
 		struct ip6_sf_list *psf;
 
-		pmc->mca_tomb = im->mca_tomb;
-		pmc->mca_sources = im->mca_sources;
-		im->mca_tomb = im->mca_sources = NULL;
-		for (psf = pmc->mca_sources; psf; psf = psf->sf_next)
+		rcu_assign_pointer(pmc->mca_tomb,
+				   rtnl_dereference(im->mca_tomb));
+		rcu_assign_pointer(pmc->mca_sources,
+				   rtnl_dereference(im->mca_sources));
+		RCU_INIT_POINTER(im->mca_tomb, NULL);
+		RCU_INIT_POINTER(im->mca_sources, NULL);
+
+		for_each_psf_rtnl(pmc, psf)
 			psf->sf_crcount = pmc->mca_crcount;
 	}
 	spin_unlock_bh(&im->mca_lock);
···
 
 static void mld_del_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
 {
-	struct ifmcaddr6 *pmc, *pmc_prev;
-	struct ip6_sf_list *psf;
+	struct ip6_sf_list *psf, *sources, *tomb;
 	struct in6_addr *pmca = &im->mca_addr;
+	struct ifmcaddr6 *pmc, *pmc_prev;
 
 	pmc_prev = NULL;
 	for (pmc = idev->mc_tomb; pmc; pmc = pmc->next) {
···
 	if (pmc) {
 		im->idev = pmc->idev;
 		if (im->mca_sfmode == MCAST_INCLUDE) {
-			swap(im->mca_tomb, pmc->mca_tomb);
-			swap(im->mca_sources, pmc->mca_sources);
-			for (psf = im->mca_sources; psf; psf = psf->sf_next)
+			tomb = rcu_replace_pointer(im->mca_tomb,
+						   rtnl_dereference(pmc->mca_tomb),
+						   lockdep_rtnl_is_held());
+			rcu_assign_pointer(pmc->mca_tomb, tomb);
+
+			sources = rcu_replace_pointer(im->mca_sources,
+						      rtnl_dereference(pmc->mca_sources),
+						      lockdep_rtnl_is_held());
+			rcu_assign_pointer(pmc->mca_sources, sources);
+			for_each_psf_rtnl(im, psf)
 				psf->sf_crcount = idev->mc_qrv;
 		} else {
 			im->mca_crcount = idev->mc_qrv;
···
 		struct ip6_sf_list *psf, *psf_next;
 
 		spin_lock_bh(&pmc->mca_lock);
-		psf = pmc->mca_tomb;
-		pmc->mca_tomb = NULL;
+		psf = rtnl_dereference(pmc->mca_tomb);
+		RCU_INIT_POINTER(pmc->mca_tomb, NULL);
 		spin_unlock_bh(&pmc->mca_lock);
 		for (; psf; psf = psf_next) {
-			psf_next = psf->sf_next;
-			kfree(psf);
+			psf_next = rtnl_dereference(psf->sf_next);
+			kfree_rcu(psf, rcu);
 		}
 	}
 	read_unlock_bh(&idev->lock);
···
 				struct ip6_sf_list *psf;
 
 				spin_lock_bh(&mc->mca_lock);
-				for (psf = mc->mca_sources; psf; psf = psf->sf_next) {
+				for_each_psf_rcu(mc, psf) {
 					if (ipv6_addr_equal(&psf->sf_addr, src_addr))
 						break;
 				}
···
 	int i, scount;
 
 	scount = 0;
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rcu(pmc, psf) {
 		if (scount == nsrcs)
 			break;
 		for (i = 0; i < nsrcs; i++) {
···
 	/* mark INCLUDE-mode sources */
 
 	scount = 0;
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rcu(pmc, psf) {
 		if (scount == nsrcs)
 			break;
 		for (i = 0; i < nsrcs; i++) {
···
 	struct ip6_sf_list *psf;
 	int scount = 0;
 
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rtnl(pmc, psf) {
 		if (!is_in(pmc, psf, type, gdeleted, sdeleted))
 			continue;
 		scount++;
···
 #define AVAILABLE(skb)	((skb) ? skb_availroom(skb) : 0)
 
 static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc,
-	int type, int gdeleted, int sdeleted, int crsend)
+				int type, int gdeleted, int sdeleted,
+				int crsend)
 {
+	struct ip6_sf_list *psf, *psf_prev, *psf_next;
+	int scount, stotal, first, isquery, truncate;
+	struct ip6_sf_list __rcu **psf_list;
 	struct inet6_dev *idev = pmc->idev;
 	struct net_device *dev = idev->dev;
-	struct mld2_report *pmr;
 	struct mld2_grec *pgr = NULL;
-	struct ip6_sf_list *psf, *psf_next, *psf_prev, **psf_list;
-	int scount, stotal, first, isquery, truncate;
+	struct mld2_report *pmr;
 	unsigned int mtu;
 
 	if (pmc->mca_flags & MAF_NOREPORT)
···
 
 	psf_list = sdeleted ? &pmc->mca_tomb : &pmc->mca_sources;
 
-	if (!*psf_list)
+	if (!rcu_access_pointer(*psf_list))
 		goto empty_source;
 
 	pmr = skb ? (struct mld2_report *)skb_transport_header(skb) : NULL;
···
 	}
 	first = 1;
 	psf_prev = NULL;
-	for (psf = *psf_list; psf; psf = psf_next) {
+	for (psf = rtnl_dereference(*psf_list);
+	     psf;
+	     psf = psf_next) {
 		struct in6_addr *psrc;
 
-		psf_next = psf->sf_next;
+		psf_next = rtnl_dereference(psf->sf_next);
 
 		if (!is_in(pmc, psf, type, gdeleted, sdeleted) && !crsend) {
 			psf_prev = psf;
···
 			psf->sf_crcount--;
 			if ((sdeleted || gdeleted) && psf->sf_crcount == 0) {
 				if (psf_prev)
-					psf_prev->sf_next = psf->sf_next;
+					rcu_assign_pointer(psf_prev->sf_next,
+							   rtnl_dereference(psf->sf_next));
 				else
-					*psf_list = psf->sf_next;
-				kfree(psf);
+					rcu_assign_pointer(*psf_list,
+							   rtnl_dereference(psf->sf_next));
+				kfree_rcu(psf, rcu);
 				continue;
 			}
 		}
···
 /*
  * remove zero-count source records from a source filter list
  */
-static void mld_clear_zeros(struct ip6_sf_list **ppsf)
+static void mld_clear_zeros(struct ip6_sf_list __rcu **ppsf)
 {
 	struct ip6_sf_list *psf_prev, *psf_next, *psf;
 
 	psf_prev = NULL;
-	for (psf = *ppsf; psf; psf = psf_next) {
-		psf_next = psf->sf_next;
+	for (psf = rtnl_dereference(*ppsf);
+	     psf;
+	     psf = psf_next) {
+		psf_next = rtnl_dereference(psf->sf_next);
 		if (psf->sf_crcount == 0) {
 			if (psf_prev)
-				psf_prev->sf_next = psf->sf_next;
+				rcu_assign_pointer(psf_prev->sf_next,
+						   rtnl_dereference(psf->sf_next));
 			else
-				*ppsf = psf->sf_next;
-			kfree(psf);
-		} else
+				rcu_assign_pointer(*ppsf,
+						   rtnl_dereference(psf->sf_next));
+			kfree_rcu(psf, rcu);
+		} else {
 			psf_prev = psf;
+		}
 	}
 }
 
···
 				mld_clear_zeros(&pmc->mca_sources);
 			}
 		}
-		if (pmc->mca_crcount == 0 && !pmc->mca_tomb &&
-		    !pmc->mca_sources) {
+		if (pmc->mca_crcount == 0 &&
+		    !rcu_access_pointer(pmc->mca_tomb) &&
+		    !rcu_access_pointer(pmc->mca_sources)) {
 			if (pmc_prev)
 				pmc_prev->next = pmc_next;
 			else
···
 	int rv = 0;
 
 	psf_prev = NULL;
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rtnl(pmc, psf) {
 		if (ipv6_addr_equal(&psf->sf_addr, psfsrc))
 			break;
 		psf_prev = psf;
···
 
 		/* no more filters for this source */
 		if (psf_prev)
-			psf_prev->sf_next = psf->sf_next;
+			rcu_assign_pointer(psf_prev->sf_next,
+					   rtnl_dereference(psf->sf_next));
 		else
-			pmc->mca_sources = psf->sf_next;
+			rcu_assign_pointer(pmc->mca_sources,
+					   rtnl_dereference(psf->sf_next));
+
 		if (psf->sf_oldin && !(pmc->mca_flags & MAF_NOREPORT) &&
 		    !mld_in_v1_mode(idev)) {
 			psf->sf_crcount = idev->mc_qrv;
-			psf->sf_next = pmc->mca_tomb;
-			pmc->mca_tomb = psf;
+			rcu_assign_pointer(psf->sf_next,
+					   rtnl_dereference(pmc->mca_tomb));
+			rcu_assign_pointer(pmc->mca_tomb, psf);
 			rv = 1;
-		} else
-			kfree(psf);
+		} else {
+			kfree_rcu(psf, rcu);
+		}
 	}
 	return rv;
 }
···
 		pmc->mca_sfmode = MCAST_INCLUDE;
 		pmc->mca_crcount = idev->mc_qrv;
 		idev->mc_ifc_count = pmc->mca_crcount;
-		for (psf = pmc->mca_sources; psf; psf = psf->sf_next)
+		for_each_psf_rtnl(pmc, psf)
 			psf->sf_crcount = 0;
 		mld_ifc_event(pmc->idev);
 	} else if (sf_setstate(pmc) || changerec)
···
 	struct ip6_sf_list *psf, *psf_prev;
 
 	psf_prev = NULL;
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rtnl(pmc, psf) {
 		if (ipv6_addr_equal(&psf->sf_addr, psfsrc))
 			break;
 		psf_prev = psf;
···
 
 		psf->sf_addr = *psfsrc;
 		if (psf_prev) {
-			psf_prev->sf_next = psf;
-		} else
-			pmc->mca_sources = psf;
+			rcu_assign_pointer(psf_prev->sf_next, psf);
+		} else {
+			rcu_assign_pointer(pmc->mca_sources, psf);
+		}
 	}
 	psf->sf_count[sfmode]++;
 	return 0;
···
 	struct ip6_sf_list *psf;
 	int mca_xcount = pmc->mca_sfcount[MCAST_EXCLUDE];
 
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next)
+	for_each_psf_rtnl(pmc, psf) {
 		if (pmc->mca_sfcount[MCAST_EXCLUDE]) {
 			psf->sf_oldin = mca_xcount ==
 				psf->sf_count[MCAST_EXCLUDE] &&
 				!psf->sf_count[MCAST_INCLUDE];
-		} else
+		} else {
 			psf->sf_oldin = psf->sf_count[MCAST_INCLUDE] != 0;
+		}
+	}
 }
 
 static int sf_setstate(struct ifmcaddr6 *pmc)
···
 	int new_in, rv;
 
 	rv = 0;
-	for (psf = pmc->mca_sources; psf; psf = psf->sf_next) {
+	for_each_psf_rtnl(pmc, psf) {
 		if (pmc->mca_sfcount[MCAST_EXCLUDE]) {
 			new_in = mca_xcount == psf->sf_count[MCAST_EXCLUDE] &&
 				!psf->sf_count[MCAST_INCLUDE];
···
 			if (!psf->sf_oldin) {
 				struct ip6_sf_list *prev = NULL;
 
-				for (dpsf = pmc->mca_tomb; dpsf;
-				     dpsf = dpsf->sf_next) {
+				for_each_psf_tomb(pmc, dpsf) {
 					if (ipv6_addr_equal(&dpsf->sf_addr,
 					    &psf->sf_addr))
 						break;
···
 				}
 				if (dpsf) {
 					if (prev)
-						prev->sf_next = dpsf->sf_next;
+						rcu_assign_pointer(prev->sf_next,
+								   rtnl_dereference(dpsf->sf_next));
 					else
-						pmc->mca_tomb = dpsf->sf_next;
-					kfree(dpsf);
+						rcu_assign_pointer(pmc->mca_tomb,
+								   rtnl_dereference(dpsf->sf_next));
+					kfree_rcu(dpsf, rcu);
 				}
 				psf->sf_crcount = qrv;
 				rv++;
···
 			 * add or update "delete" records if an active filter
 			 * is now inactive
 			 */
-			for (dpsf = pmc->mca_tomb; dpsf; dpsf = dpsf->sf_next)
+
+			for_each_psf_tomb(pmc, dpsf)
 				if (ipv6_addr_equal(&dpsf->sf_addr,
 				    &psf->sf_addr))
 					break;
···
 				if (!dpsf)
 					continue;
 				*dpsf = *psf;
-				/* pmc->mca_lock held by callers */
-				dpsf->sf_next = pmc->mca_tomb;
-				pmc->mca_tomb = dpsf;
+				rcu_assign_pointer(dpsf->sf_next,
+						   rtnl_dereference(pmc->mca_tomb));
+				rcu_assign_pointer(pmc->mca_tomb, dpsf);
 			}
 			dpsf->sf_crcount = qrv;
 			rv++;
···
 
 		pmc->mca_crcount = idev->mc_qrv;
 		idev->mc_ifc_count = pmc->mca_crcount;
-		for (psf = pmc->mca_sources; psf; psf = psf->sf_next)
+		for_each_psf_rtnl(pmc, psf)
 			psf->sf_crcount = 0;
 		mld_ifc_event(idev);
 	} else if (sf_setstate(pmc))
···
 {
 	struct ip6_sf_list *psf, *nextpsf;
 
-	for (psf = pmc->mca_tomb; psf; psf = nextpsf) {
-		nextpsf = psf->sf_next;
-		kfree(psf);
+	for (psf = rtnl_dereference(pmc->mca_tomb);
+	     psf;
+	     psf = nextpsf) {
+		nextpsf = rtnl_dereference(psf->sf_next);
+		kfree_rcu(psf, rcu);
 	}
-	pmc->mca_tomb = NULL;
-	for (psf = pmc->mca_sources; psf; psf = nextpsf) {
-		nextpsf = psf->sf_next;
-		kfree(psf);
+	RCU_INIT_POINTER(pmc->mca_tomb, NULL);
+	for (psf = rtnl_dereference(pmc->mca_sources);
+	     psf;
+	     psf = nextpsf) {
+		nextpsf = rtnl_dereference(psf->sf_next);
+		kfree_rcu(psf, rcu);
 	}
-	pmc->mca_sources = NULL;
+	RCU_INIT_POINTER(pmc->mca_sources, NULL);
 	pmc->mca_sfmode = MCAST_EXCLUDE;
 	pmc->mca_sfcount[MCAST_INCLUDE] = 0;
 	pmc->mca_sfcount[MCAST_EXCLUDE] = 1;
···
 		im = idev->mc_list;
 		if (likely(im)) {
 			spin_lock_bh(&im->mca_lock);
-			psf = im->mca_sources;
+			psf = rcu_dereference(im->mca_sources);
 			if (likely(psf)) {
 				state->im = im;
 				state->idev = idev;
···
 {
 	struct igmp6_mcf_iter_state *state = igmp6_mcf_seq_private(seq);
 
-	psf = psf->sf_next;
+	psf = rcu_dereference(psf->sf_next);
 	while (!psf) {
 		spin_unlock_bh(&state->im->mca_lock);
 		state->im = state->im->next;
···
 		if (!state->im)
 			break;
 		spin_lock_bh(&state->im->mca_lock);
-		psf = state->im->mca_sources;
+		psf = rcu_dereference(state->im->mca_sources);
 	}
 out:
 	return psf;