svn commit: r368009 - head/sys/kern

[Kyle Evans]

Author: kevans
Date: Wed Nov 25 01:42:32 2020
New Revision: 368009
URL: https://svnweb.freebsd.org/changeset/base/368009

Log:
  kern: cpuset: allow cpuset_create() to take an allocated *setp
  
  Currently, it must always allocate a new set to be used for passing to
  _cpuset_create, but it doesn't have to. This is purely kern_cpuset.c
  internal and it's sparsely used, so just change it to use *setp if it's
  not-NULL and modify the two consumers to pass in the address of a NULL
  cpuset.
  
  This paves the way for consumers that want the unr allocation without the
  possibility of sleeping as long as they've done their due diligence to
  ensure that the mask will properly apply atop the supplied parent
  (i.e. avoiding the free_unr() in the last failure path).
  
  Reviewed by:	jamie, markj
  MFC after:	1 week
  Differential Revision:	https://reviews.freebsd.org/D27297

Modified:
  head/sys/kern/kern_cpuset.c

Modified: head/sys/kern/kern_cpuset.c
==============================================================================
--- head/sys/kern/kern_cpuset.c	Wed Nov 25 01:31:00 2020	(r368008)
+++ head/sys/kern/kern_cpuset.c	Wed Nov 25 01:42:32 2020	(r368009)
@@ -326,6 +326,10 @@ _cpuset_create(struct cpuset *set, struct cpuset *pare
  * Create a new non-anonymous set with the requested parent and mask.  May
  * return failures if the mask is invalid or a new number can not be
  * allocated.
+ *
+ * If *setp is not NULL, then it will be used as-is.  The caller must take
+ * into account that *setp will be inserted at the head of cpuset_ids and
+ * plan any potentially conflicting cs_link usage accordingly.
  */
 static int
 cpuset_create(struct cpuset **setp, struct cpuset *parent, const cpuset_t *mask)
@@ -333,16 +337,22 @@ cpuset_create(struct cpuset **setp, struct cpuset *par
 	struct cpuset *set;
 	cpusetid_t id;
 	int error;
+	bool dofree;
 
 	id = alloc_unr(cpuset_unr);
 	if (id == -1)
 		return (ENFILE);
-	*setp = set = uma_zalloc(cpuset_zone, M_WAITOK | M_ZERO);
+	dofree = (*setp == NULL);
+	if (*setp != NULL)
+		set = *setp;
+	else
+		*setp = set = uma_zalloc(cpuset_zone, M_WAITOK | M_ZERO);
 	error = _cpuset_create(set, parent, mask, NULL, id);
 	if (error == 0)
 		return (0);
 	free_unr(cpuset_unr, id);
-	uma_zfree(cpuset_zone, set);
+	if (dofree)
+		uma_zfree(cpuset_zone, set);
 
 	return (error);
 }
@@ -1552,16 +1562,17 @@ cpuset_create_root(struct prison *pr, struct cpuset **
 	KASSERT(pr != NULL, ("[%s:%d] invalid pr", __func__, __LINE__));
 	KASSERT(setp != NULL, ("[%s:%d] invalid setp", __func__, __LINE__));
 
-	error = cpuset_create(setp, pr->pr_cpuset, &pr->pr_cpuset->cs_mask);
+	set = NULL;
+	error = cpuset_create(&set, pr->pr_cpuset, &pr->pr_cpuset->cs_mask);
 	if (error)
 		return (error);
 
-	KASSERT(*setp != NULL, ("[%s:%d] cpuset_create returned invalid data",
+	KASSERT(set != NULL, ("[%s:%d] cpuset_create returned invalid data",
 	    __func__, __LINE__));
 
 	/* Mark the set as root. */
-	set = *setp;
 	set->cs_flags |= CPU_SET_ROOT;
+	*setp = set;
 
 	return (0);
 }
@@ -1618,6 +1629,7 @@ sys_cpuset(struct thread *td, struct cpuset_args *uap)
 	thread_lock(td);
 	root = cpuset_refroot(td->td_cpuset);
 	thread_unlock(td);
+	set = NULL;
 	error = cpuset_create(&set, root, &root->cs_mask);
 	cpuset_rel(root);
 	if (error)