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Date:      Fri, 20 Apr 2018 14:47:02 +0000 (UTC)
From:      "Jonathan T. Looney" <jtl@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org
Subject:   svn commit: r332821 - in stable/11/sys: netinet netinet6
Message-ID:  <201804201447.w3KEl2Vr066261@repo.freebsd.org>

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Author: jtl
Date: Fri Apr 20 14:47:02 2018
New Revision: 332821
URL: https://svnweb.freebsd.org/changeset/base/332821

Log:
  MFC r331309:
    If the INP lock is uncontested, avoid taking a reference and jumping
    through the lock-switching hoops.
  
    A few of the INP lookup operations that lock INPs after the lookup do
    so using this mechanism (to maintain lock ordering):
  
    1. Lock lookup structure.
    2. Find INP.
    3. Acquire reference on INP.
    4. Drop lock on lookup structure.
    5. Acquire INP lock.
    6. Drop reference on INP.
  
    This change provides a slightly shorter path for cases where the INP
    lock is uncontested:
  
    1. Lock lookup structure.
    2. Find INP.
    3. Try to acquire the INP lock.
    4. If successful, drop lock on lookup structure.
  
    Of course, if the INP lock is contested, the functions will need to
    revert to the previous way of switching locks safely.
  
    This saves a few atomic operations when the INP lock is uncontested.
  
  Sponsored by:	Netflix, Inc.

Modified:
  stable/11/sys/netinet/in_pcb.c
  stable/11/sys/netinet6/in6_pcb.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/netinet/in_pcb.c
==============================================================================
--- stable/11/sys/netinet/in_pcb.c	Fri Apr 20 14:34:04 2018	(r332820)
+++ stable/11/sys/netinet/in_pcb.c	Fri Apr 20 14:47:02 2018	(r332821)
@@ -1619,6 +1619,7 @@ in_pcblookup_group(struct inpcbinfo *pcbinfo, struct i
 	struct inpcbhead *head;
 	struct inpcb *inp, *tmpinp;
 	u_short fport = fport_arg, lport = lport_arg;
+	bool locked;
 
 	/*
 	 * First look for an exact match.
@@ -1805,18 +1806,32 @@ in_pcblookup_group(struct inpcbinfo *pcbinfo, struct i
 	return (NULL);
 
 found:
-	in_pcbref(inp);
-	INP_GROUP_UNLOCK(pcbgroup);
-	if (lookupflags & INPLOOKUP_WLOCKPCB) {
-		INP_WLOCK(inp);
-		if (in_pcbrele_wlocked(inp))
-			return (NULL);
-	} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
-		INP_RLOCK(inp);
-		if (in_pcbrele_rlocked(inp))
-			return (NULL);
-	} else
+	if (lookupflags & INPLOOKUP_WLOCKPCB)
+		locked = TRY_INP_WLOCK(inp);
+	else if (lookupflags & INPLOOKUP_RLOCKPCB)
+		locked = TRY_INP_RLOCK(inp);
+	else
 		panic("%s: locking bug", __func__);
+	if (!locked)
+		in_pcbref(inp);
+	INP_GROUP_UNLOCK(pcbgroup);
+	if (!locked) {
+		if (lookupflags & INPLOOKUP_WLOCKPCB) {
+			INP_WLOCK(inp);
+			if (in_pcbrele_wlocked(inp))
+				return (NULL);
+		} else {
+			INP_RLOCK(inp);
+			if (in_pcbrele_rlocked(inp))
+				return (NULL);
+		}
+	}
+#ifdef INVARIANTS
+	if (lookupflags & INPLOOKUP_WLOCKPCB)
+		INP_WLOCK_ASSERT(inp);
+	else
+		INP_RLOCK_ASSERT(inp);
+#endif
 	return (inp);
 }
 #endif /* PCBGROUP */
@@ -1955,23 +1970,38 @@ in_pcblookup_hash(struct inpcbinfo *pcbinfo, struct in
     struct ifnet *ifp)
 {
 	struct inpcb *inp;
+	bool locked;
 
 	INP_HASH_RLOCK(pcbinfo);
 	inp = in_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
 	    (lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp);
 	if (inp != NULL) {
-		in_pcbref(inp);
-		INP_HASH_RUNLOCK(pcbinfo);
-		if (lookupflags & INPLOOKUP_WLOCKPCB) {
-			INP_WLOCK(inp);
-			if (in_pcbrele_wlocked(inp))
-				return (NULL);
-		} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
-			INP_RLOCK(inp);
-			if (in_pcbrele_rlocked(inp))
-				return (NULL);
-		} else
+		if (lookupflags & INPLOOKUP_WLOCKPCB)
+			locked = INP_TRY_WLOCK(inp);
+		else if (lookupflags & INPLOOKUP_RLOCKPCB)
+			locked = INP_TRY_RLOCK(inp);
+		else
 			panic("%s: locking bug", __func__);
+		if (!locked)
+			in_pcbref(inp);
+		INP_HASH_RUNLOCK(pcbinfo);
+		if (!locked) {
+			if (lookupflags & INPLOOKUP_WLOCKPCB) {
+				INP_WLOCK(inp);
+				if (in_pcbrele_wlocked(inp))
+					return (NULL);
+			} else {
+				INP_RLOCK(inp);
+				if (in_pcbrele_rlocked(inp))
+					return (NULL);
+			}
+		}
+#ifdef INVARIANTS
+		if (lookupflags & INPLOOKUP_WLOCKPCB)
+			INP_WLOCK_ASSERT(inp);
+		else
+			INP_RLOCK_ASSERT(inp);
+#endif
 	} else
 		INP_HASH_RUNLOCK(pcbinfo);
 	return (inp);

Modified: stable/11/sys/netinet6/in6_pcb.c
==============================================================================
--- stable/11/sys/netinet6/in6_pcb.c	Fri Apr 20 14:34:04 2018	(r332820)
+++ stable/11/sys/netinet6/in6_pcb.c	Fri Apr 20 14:47:02 2018	(r332821)
@@ -866,6 +866,7 @@ in6_pcblookup_group(struct inpcbinfo *pcbinfo, struct 
 	struct inpcbhead *head;
 	struct inpcb *inp, *tmpinp;
 	u_short fport = fport_arg, lport = lport_arg;
+	bool locked;
 
 	/*
 	 * First look for an exact match.
@@ -1024,18 +1025,32 @@ in6_pcblookup_group(struct inpcbinfo *pcbinfo, struct 
 	return (NULL);
 
 found:
-	in_pcbref(inp);
-	INP_GROUP_UNLOCK(pcbgroup);
-	if (lookupflags & INPLOOKUP_WLOCKPCB) {
-		INP_WLOCK(inp);
-		if (in_pcbrele_wlocked(inp))
-			return (NULL);
-	} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
-		INP_RLOCK(inp);
-		if (in_pcbrele_rlocked(inp))
-			return (NULL);
-	} else
+	if (lookupflags & INPLOOKUP_WLOCKPCB)
+		locked = INP_TRY_WLOCK(inp);
+	else if (lookupflags & INPLOOKUP_RLOCKPCB)
+		locked = INP_TRY_RLOCK(inp);
+	else
 		panic("%s: locking buf", __func__);
+	if (!locked)
+		in_pcbref(inp);
+	INP_GROUP_UNLOCK(pcbgroup);
+	if (!locked) {
+		if (lookupflags & INPLOOKUP_WLOCKPCB) {
+			INP_WLOCK(inp);
+			if (in_pcbrele_wlocked(inp))
+				return (NULL);
+		} else {
+			INP_RLOCK(inp);
+			if (in_pcbrele_rlocked(inp))
+				return (NULL);
+		}
+	}
+#ifdef INVARIANTS
+	if (lookupflags & INPLOOKUP_WLOCKPCB)
+		INP_WLOCK_ASSERT(inp);
+	else
+		INP_RLOCK_ASSERT(inp);
+#endif
 	return (inp);
 }
 #endif /* PCBGROUP */
@@ -1161,23 +1176,38 @@ in6_pcblookup_hash(struct inpcbinfo *pcbinfo, struct i
     struct ifnet *ifp)
 {
 	struct inpcb *inp;
+	bool locked;
 
 	INP_HASH_RLOCK(pcbinfo);
 	inp = in6_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
 	    (lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp);
 	if (inp != NULL) {
-		in_pcbref(inp);
-		INP_HASH_RUNLOCK(pcbinfo);
-		if (lookupflags & INPLOOKUP_WLOCKPCB) {
-			INP_WLOCK(inp);
-			if (in_pcbrele_wlocked(inp))
-				return (NULL);
-		} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
-			INP_RLOCK(inp);
-			if (in_pcbrele_rlocked(inp))
-				return (NULL);
-		} else
+		if (lookupflags & INPLOOKUP_WLOCKPCB)
+			locked = INP_TRY_WLOCK(inp);
+		else if (lookupflags & INPLOOKUP_RLOCKPCB)
+			locked = INP_TRY_RLOCK(inp);
+		else
 			panic("%s: locking bug", __func__);
+		if (!locked)
+			in_pcbref(inp);
+		INP_HASH_RUNLOCK(pcbinfo);
+		if (!locked) {
+			if (lookupflags & INPLOOKUP_WLOCKPCB) {
+				INP_WLOCK(inp);
+				if (in_pcbrele_wlocked(inp))
+					return (NULL);
+			} else {
+				INP_RLOCK(inp);
+				if (in_pcbrele_rlocked(inp))
+					return (NULL);
+			}
+		}
+#ifdef INVARIANTS
+		if (lookupflags & INPLOOKUP_WLOCKPCB)
+			INP_WLOCK_ASSERT(inp);
+		else
+			INP_RLOCK_ASSERT(inp);
+#endif
 	} else
 		INP_HASH_RUNLOCK(pcbinfo);
 	return (inp);



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