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From: Andriy Voskoboinyk <avos@FreeBSD.org>
Date: Mon, 16 Oct 2017 21:21:31 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r324672 - head/sys/net
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Author: avos
Date: Mon Oct 16 21:21:31 2017
New Revision: 324672
URL: https://svnweb.freebsd.org/changeset/base/324672

Log:
  ifnet(9): split ifc_alloc_unit() (should simplify code flow)
  
  Allocate smallest unit number from pool via ifc_alloc_unit_next()
  and exact unit number (if available) via ifc_alloc_unit_specific().
  
  While here, address possible deadlock (mentioned in PR).
  
  PR:		217401
  MFC after:	5 days
  Differential Revision:	https://reviews.freebsd.org/D12551

Modified:
  head/sys/net/if_clone.c

Modified: head/sys/net/if_clone.c
==============================================================================
--- head/sys/net/if_clone.c	Mon Oct 16 20:21:51 2017	(r324671)
+++ head/sys/net/if_clone.c	Mon Oct 16 21:21:31 2017	(r324672)
@@ -595,44 +595,56 @@ ifc_name2unit(const char *name, int *unit)
 	return (0);
 }
 
-int
-ifc_alloc_unit(struct if_clone *ifc, int *unit)
+static int
+ifc_alloc_unit_specific(struct if_clone *ifc, int *unit)
 {
 	char name[IFNAMSIZ];
-	int wildcard;
 
-	wildcard = (*unit < 0);
-retry:
 	if (*unit > ifc->ifc_maxunit)
 		return (ENOSPC);
-	if (*unit < 0) {
-		*unit = alloc_unr(ifc->ifc_unrhdr);
-		if (*unit == -1)
-			return (ENOSPC);
-	} else {
-		*unit = alloc_unr_specific(ifc->ifc_unrhdr, *unit);
-		if (*unit == -1) {
-			if (wildcard) {
-				(*unit)++;
-				goto retry;
-			} else
-				return (EEXIST);
-		}
-	}
 
+	if (alloc_unr_specific(ifc->ifc_unrhdr, *unit) == -1)
+		return (EEXIST);
+
 	snprintf(name, IFNAMSIZ, "%s%d", ifc->ifc_name, *unit);
 	if (ifunit(name) != NULL) {
 		free_unr(ifc->ifc_unrhdr, *unit);
-		if (wildcard) {
-			(*unit)++;
-			goto retry;
-		} else
-			return (EEXIST);
+		return (EEXIST);
 	}
 
 	IF_CLONE_ADDREF(ifc);
 
 	return (0);
+}
+
+static int
+ifc_alloc_unit_next(struct if_clone *ifc, int *unit)
+{
+	int error;
+
+	*unit = alloc_unr(ifc->ifc_unrhdr);
+	if (*unit == -1)
+		return (ENOSPC);
+
+	free_unr(ifc->ifc_unrhdr, *unit);
+	for (;;) {
+		error = ifc_alloc_unit_specific(ifc, unit);
+		if (error != EEXIST)
+			break;
+
+		(*unit)++;
+	}
+
+	return (error);
+}
+
+int
+ifc_alloc_unit(struct if_clone *ifc, int *unit)
+{
+	if (*unit < 0)
+		return (ifc_alloc_unit_next(ifc, unit));
+	else
+		return (ifc_alloc_unit_specific(ifc, unit));
 }
 
 void