2.6.25-rc7

 kernel

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 50f5dc4..a1b61f4 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -38,7 +38,6 @@
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/pagemap.h>
-#include <linux/prio_heap.h>
 #include <linux/proc_fs.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
@@ -56,6 +55,8 @@
 #include <asm/atomic.h>
 #include <linux/mutex.h>
 #include <linux/kfifo.h>
+#include <linux/workqueue.h>
+#include <linux/cgroup.h>
 
 /*
  * Tracks how many cpusets are currently defined in system.
@@ -64,7 +65,7 @@
  */
 int number_of_cpusets __read_mostly;
 
-/* Retrieve the cpuset from a cgroup */
+/* Forward declare cgroup structures */
 struct cgroup_subsys cpuset_subsys;
 struct cpuset;
 
@@ -96,6 +97,9 @@ struct cpuset {
 
    /* partition number for rebuild_sched_domains() */
    int pn;
+
+   /* used for walking a cpuset heirarchy */
+   struct list_head stack_list;
 };
 
 /* Retrieve the cpuset for a cgroup */
@@ -111,7 +115,10 @@ static inline struct cpuset *task_cs(struct task_struct *task)
    return container_of(task_subsys_state(task, cpuset_subsys_id),
              struct cpuset, css);
 }
-
+struct cpuset_hotplug_scanner {
+   struct cgroup_scanner scan;
+   struct cgroup *to;
+};
 
 /* bits in struct cpuset flags field */
 typedef enum {
@@ -160,17 +167,17 @@ static inline int is_spread_slab(const struct cpuset *cs)
  * number, and avoid having to lock and reload mems_allowed unless
  * the cpuset they're using changes generation.
  *
- * A single, global generation is needed because attach_task() could
+ * A single, global generation is needed because cpuset_attach_task() could
  * reattach a task to a different cpuset, which must not have its
  * generation numbers aliased with those of that tasks previous cpuset.
  *
  * Generations are needed for mems_allowed because one task cannot
- * modify anothers memory placement.  So we must enable every task,
+ * modify another's memory placement.  So we must enable every task,
  * on every visit to __alloc_pages(), to efficiently check whether
  * its current->cpuset->mems_allowed has changed, requiring an update
  * of its current->mems_allowed.
  *
- * Since cpuset_mems_generation is guarded by manage_mutex,
+ * Since writes to cpuset_mems_generation are guarded by the cgroup lock
  * there is no need to mark it atomic.
  */
 static int cpuset_mems_generation;
@@ -182,17 +189,20 @@ static struct cpuset top_cpuset = {
 };
 
 /*
- * We have two global cpuset mutexes below.  They can nest.
- * It is ok to first take manage_mutex, then nest callback_mutex.  We also
- * require taking task_lock() when dereferencing a tasks cpuset pointer.
- * See "The task_lock() exception", at the end of this comment.
+ * There are two global mutexes guarding cpuset structures.  The first
+ * is the main control groups cgroup_mutex, accessed via
+ * cgroup_lock()/cgroup_unlock().  The second is the cpuset-specific
+ * callback_mutex, below. They can nest.  It is ok to first take
+ * cgroup_mutex, then nest callback_mutex.  We also require taking
+ * task_lock() when dereferencing a task's cpuset pointer.  See "The
+ * task_lock() exception", at the end of this comment.
  *
  * A task must hold both mutexes to modify cpusets.  If a task
- * holds manage_mutex, then it blocks others wanting that mutex,
+ * holds cgroup_mutex, then it blocks others wanting that mutex,
  * ensuring that it is the only task able to also acquire callback_mutex
  * and be able to modify cpusets.  It can perform various checks on
  * the cpuset structure first, knowing nothing will change.  It can
- * also allocate memory while just holding manage_mutex.  While it is
+ * also allocate memory while just holding cgroup_mutex.  While it is
  * performing these checks, various callback routines can briefly
  * acquire callback_mutex to query cpusets.  Once it is ready to make
  * the changes, it takes callback_mutex, blocking everyone else.
@@ -208,60 +218,16 @@ static struct cpuset top_cpuset = {
  * The task_struct fields mems_allowed and mems_generation may only
  * be accessed in the context of that task, so require no locks.
  *
- * Any task can increment and decrement the count field without lock.
- * So in general, code holding manage_mutex or callback_mutex can't rely
- * on the count field not changing.  However, if the count goes to
- * zero, then only attach_task(), which holds both mutexes, can
- * increment it again.  Because a count of zero means that no tasks
- * are currently attached, therefore there is no way a task attached
- * to that cpuset can fork (the other way to increment the count).
- * So code holding manage_mutex or callback_mutex can safely assume that
- * if the count is zero, it will stay zero.  Similarly, if a task
- * holds manage_mutex or callback_mutex on a cpuset with zero count, it
- * knows that the cpuset won't be removed, as cpuset_rmdir() needs
- * both of those mutexes.
- *
  * The cpuset_common_file_write handler for operations that modify
- * the cpuset hierarchy holds manage_mutex across the entire operation,
+ * the cpuset hierarchy holds cgroup_mutex across the entire operation,
  * single threading all such cpuset modifications across the system.
  *
  * The cpuset_common_file_read() handlers only hold callback_mutex across
  * small pieces of code, such as when reading out possibly multi-word
  * cpumasks and nodemasks.
  *
- * The fork and exit callbacks cpuset_fork() and cpuset_exit(), don't
- * (usually) take either mutex.  These are the two most performance
- * critical pieces of code here.  The exception occurs on cpuset_exit(),
- * when a task in a notify_on_release cpuset exits.  Then manage_mutex
- * is taken, and if the cpuset count is zero, a usermode call made
- * to /sbin/cpuset_release_agent with the name of the cpuset (path
- * relative to the root of cpuset file system) as the argument.
- *
- * A cpuset can only be deleted if both its 'count' of using tasks
- * is zero, and its list of 'children' cpusets is empty.  Since all
- * tasks in the system use _some_ cpuset, and since there is always at
- * least one task in the system (init), therefore, top_cpuset
- * always has either children cpusets and/or using tasks.  So we don't
- * need a special hack to ensure that top_cpuset cannot be deleted.
- *
- * The above "Tale of Two Semaphores" would be complete, but for:
- *
- *   The task_lock() exception
- *
- * The need for this exception arises from the action of attach_task(),
- * which overwrites one tasks cpuset pointer with another.  It does
- * so using both mutexes, however there are several performance
- * critical places that need to reference task->cpuset without the
- * expense of grabbing a system global mutex.  Therefore except as
- * noted below, when dereferencing or, as in attach_task(), modifying
- * a tasks cpuset pointer we use task_lock(), which acts on a spinlock
- * (task->alloc_lock) already in the task_struct routinely used for
- * such matters.
- *
- * P.S.  One more locking exception.  RCU is used to guard the
- * update of a tasks cpuset pointer by attach_task() and the
- * access of task->cpuset->mems_generation via that pointer in
- * the routine cpuset_update_task_memory_state().
+ * Accessing a task's cpuset should be done in accordance with the
+ * guidelines for accessing subsystem state in kernel/cgroup.c
  */
 
 static DEFINE_MUTEX(callback_mutex);
@@ -354,15 +320,14 @@ static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
  * Do not call this routine if in_interrupt().
  *
  * Call without callback_mutex or task_lock() held.  May be
- * called with or without manage_mutex held.  Thanks in part to
- * 'the_top_cpuset_hack', the tasks cpuset pointer will never
- * be NULL.  This routine also might acquire callback_mutex and
- * current->mm->mmap_sem during call.
+ * called with or without cgroup_mutex held.  Thanks in part to
+ * 'the_top_cpuset_hack', the task's cpuset pointer will never
+ * be NULL.  This routine also might acquire callback_mutex during
+ * call.
  *
  * Reading current->cpuset->mems_generation doesn't need task_lock
  * to guard the current->cpuset derefence, because it is guarded
- * from concurrent freeing of current->cpuset by attach_task(),
- * using RCU.
+ * from concurrent freeing of current->cpuset using RCU.
  *
  * The rcu_dereference() is technically probably not needed,
  * as I don't actually mind if I see a new cpuset pointer but
@@ -424,7 +389,7 @@ void cpuset_update_task_memory_state(void)
  *
  * One cpuset is a subset of another if all its allowed CPUs and
  * Memory Nodes are a subset of the other, and its exclusive flags
- * are only set if the other's are set.  Call holding manage_mutex.
+ * are only set if the other's are set.  Call holding cgroup_mutex.
  */
 
 static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
@@ -442,7 +407,7 @@ static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
  * If we replaced the flag and mask values of the current cpuset
  * (cur) with those values in the trial cpuset (trial), would
  * our various subset and exclusive rules still be valid?  Presumes
- * manage_mutex held.
+ * cgroup_mutex held.
  *
  * 'cur' is the address of an actual, in-use cpuset.  Operations
  * such as list traversal that depend on the actual address of the
@@ -476,7 +441,10 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
    if (!is_cpuset_subset(trial, par))
       return -EACCES;
 
-   /* If either I or some sibling (!= me) is exclusive, we can't overlap */
+   /*
+    * If either I or some sibling (!= me) is exclusive, we can't
+    * overlap
+    */
    list_for_each_entry(cont, &par->css.cgroup->children, sibling) {
       c = cgroup_cs(cont);
       if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
@@ -537,10 +505,10 @@ static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
  *
  * Call with cgroup_mutex held.  May take callback_mutex during
  * call due to the kfifo_alloc() and kmalloc() calls.  May nest
- * a call to the lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
+ * a call to the get_online_cpus()/put_online_cpus() pair.
  * Must not be called holding callback_mutex, because we must not
- * call lock_cpu_hotplug() while holding callback_mutex.  Elsewhere
- * the kernel nests callback_mutex inside lock_cpu_hotplug() calls.
+ * call get_online_cpus() while holding callback_mutex.  Elsewhere
+ * the kernel nests callback_mutex inside get_online_cpus() calls.
  * So the reverse nesting would risk an ABBA deadlock.
  *
  * The three key local variables below are:
@@ -691,9 +659,9 @@ restart:
 
 rebuild:
    /* Have scheduler rebuild sched domains */
-   lock_cpu_hotplug();
+   get_online_cpus();
    partition_sched_domains(ndoms, doms);
-   unlock_cpu_hotplug();
+   put_online_cpus();
 
 done:
    if (q && !IS_ERR(q))
@@ -732,22 +700,50 @@ static inline int started_after(void *p1, void *p2)
    return started_after_time(t1, &t2->start_time, t2);
 }
 
-/*
- * Call with manage_mutex held.  May take callback_mutex during call.
+/**
+ * cpuset_test_cpumask - test a task's cpus_allowed versus its cpuset's
+ * @tsk: task to test
+ * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
+ *
+ * Call with cgroup_mutex held.  May take callback_mutex during call.
+ * Called for each task in a cgroup by cgroup_scan_tasks().
+ * Return nonzero if this tasks's cpus_allowed mask should be changed (in other
+ * words, if its mask is not equal to its cpuset's mask).
+ */
+int cpuset_test_cpumask(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+   return !cpus_equal(tsk->cpus_allowed,
+         (cgroup_cs(scan->cg))->cpus_allowed);
+}
+
+/**
+ * cpuset_change_cpumask - make a task's cpus_allowed the same as its cpuset's
+ * @tsk: task to test
+ * @scan: struct cgroup_scanner containing the cgroup of the task
+ *
+ * Called by cgroup_scan_tasks() for each task in a cgroup whose
+ * cpus_allowed mask needs to be changed.
+ *
+ * We don't need to re-check for the cgroup/cpuset membership, since we're
+ * holding cgroup_lock() at this point.
  */
+void cpuset_change_cpumask(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+   set_cpus_allowed(tsk, (cgroup_cs(scan->cg))->cpus_allowed);
+}
 
+/**
+ * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
+ * @cs: the cpuset to consider
+ * @buf: buffer of cpu numbers written to this cpuset
+ */
 static int update_cpumask(struct cpuset *cs, char *buf)
 {
    struct cpuset trialcs;
-   int retval, i;
-   int is_load_balanced;
-   struct cgroup_iter it;
-   struct cgroup *cgrp = cs->css.cgroup;
-   struct task_struct *p, *dropped;
-   /* Never dereference latest_task, since it's not refcounted */
-   struct task_struct *latest_task = NULL;
+   struct cgroup_scanner scan;
    struct ptr_heap heap;
-   struct timespec latest_time = { 0, 0 };
+   int retval;
+   int is_load_balanced;
 
    /* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
    if (cs == &top_cpuset)
@@ -756,7 +752,7 @@ static int update_cpumask(struct cpuset *cs, char *buf)
    trialcs = *cs;
 
    /*
-    * An empty cpus_allowed is ok iff there are no tasks in the cpuset.
+    * An empty cpus_allowed is ok only if the cpuset has no tasks.
     * Since cpulist_parse() fails on an empty mask, we special case
     * that parsing.  The validate_change() call ensures that cpusets
     * with tasks have cpus.
@@ -777,6 +773,7 @@ static int update_cpumask(struct cpuset *cs, char *buf)
    /* Nothing to do if the cpus didn't change */
    if (cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed))
       return 0;
+
    retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, &started_after);
    if (retval)
       return retval;
@@ -787,62 +784,19 @@ static int update_cpumask(struct cpuset *cs, char *buf)
    cs->cpus_allowed = trialcs.cpus_allowed;
    mutex_unlock(&callback_mutex);
 
- again:
    /*
     * Scan tasks in the cpuset, and update the cpumasks of any
-    * that need an update. Since we can't call set_cpus_allowed()
-    * while holding tasklist_lock, gather tasks to be processed
-    * in a heap structure. If the statically-sized heap fills up,
-    * overflow tasks that started later, and in future iterations
-    * only consider tasks that started after the latest task in
-    * the previous pass. This guarantees forward progress and
-    * that we don't miss any tasks
+    * that need an update.
     */
-   heap.size = 0;
-   cgroup_iter_start(cgrp, &it);
-   while ((p = cgroup_iter_next(cgrp, &it))) {
-      /* Only affect tasks that don't have the right cpus_allowed */
-      if (cpus_equal(p->cpus_allowed, cs->cpus_allowed))
-         continue;
-      /*
-       * Only process tasks that started after the last task
-       * we processed
-       */
-      if (!started_after_time(p, &latest_time, latest_task))
-         continue;
-      dropped = heap_insert(&heap, p);
-      if (dropped == NULL) {
-         get_task_struct(p);
-      } else if (dropped != p) {
-         get_task_struct(p);
-         put_task_struct(dropped);
-      }
-   }
-   cgroup_iter_end(cgrp, &it);
-   if (heap.size) {
-      for (i = 0; i < heap.size; i++) {
-         struct task_struct *p = heap.ptrs[i];
-         if (i == 0) {
-            latest_time = p->start_time;
-            latest_task = p;
-         }
-         set_cpus_allowed(p, cs->cpus_allowed);
-         put_task_struct(p);
-      }
-      /*
-       * If we had to process any tasks at all, scan again
-       * in case some of them were in the middle of forking
-       * children that didn't notice the new cpumask
-       * restriction.  Not the most efficient way to do it,
-       * but it avoids having to take callback_mutex in the
-       * fork path
-       */
-      goto again;
-   }
+   scan.cg = cs->css.cgroup;
+   scan.test_task = cpuset_test_cpumask;
+   scan.process_task = cpuset_change_cpumask;
+   scan.heap = &heap;
+   cgroup_scan_tasks(&scan);
    heap_free(&heap);
+
    if (is_load_balanced)
       rebuild_sched_domains();
-
    return 0;
 }
 
@@ -854,11 +808,11 @@ static int update_cpumask(struct cpuset *cs, char *buf)
  *    Temporarilly set tasks mems_allowed to target nodes of migration,
  *    so that the migration code can allocate pages on these nodes.
  *
- *    Call holding manage_mutex, so our current->cpuset won't change
- *    during this call, as manage_mutex holds off any attach_task()
+ *    Call holding cgroup_mutex, so current's cpuset won't change
+ *    during this call, as manage_mutex holds off any cpuset_attach()
  *    calls.  Therefore we don't need to take task_lock around the
  *    call to guarantee_online_mems(), as we know no one is changing
- *    our tasks cpuset.
+ *    our task's cpuset.
  *
  *    Hold callback_mutex around the two modifications of our tasks
  *    mems_allowed to synchronize with cpuset_mems_allowed().
@@ -903,7 +857,7 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
  * the cpuset is marked 'memory_migrate', migrate the tasks
  * pages to the new memory.
  *
- * Call with manage_mutex held.  May take callback_mutex during call.
+ * Call with cgroup_mutex held.  May take callback_mutex during call.
  * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
  * lock each such tasks mm->mmap_sem, scan its vma's and rebind
  * their mempolicies to the cpusets new mems_allowed.
@@ -1016,7 +970,7 @@ static int update_nodemask(struct cpuset *cs, char *buf)
     * tasklist_lock.  Forks can happen again now - the mpol_copy()
     * cpuset_being_rebound check will catch such forks, and rebind
     * their vma mempolicies too.  Because we still hold the global
-    * cpuset manage_mutex, we know that no other rebind effort will
+    * cgroup_mutex, we know that no other rebind effort will
     * be contending for the global variable cpuset_being_rebound.
     * It's ok if we rebind the same mm twice; mpol_rebind_mm()
     * is idempotent.  Also migrate pages in each mm to new nodes.
@@ -1031,7 +985,7 @@ static int update_nodemask(struct cpuset *cs, char *buf)
       mmput(mm);
    }
 
-   /* We're done rebinding vma's to this cpusets new mems_allowed. */
+   /* We're done rebinding vmas to this cpuset's new mems_allowed. */
    kfree(mmarray);
    cpuset_being_rebound = NULL;
    retval = 0;
@@ -1045,7 +999,7 @@ int current_cpuset_is_being_rebound(void)
 }
 
 /*
- * Call with manage_mutex held.
+ * Call with cgroup_mutex held.
  */
 
 static int update_memory_pressure_enabled(struct cpuset *cs, char *buf)
@@ -1066,7 +1020,7 @@ static int update_memory_pressure_enabled(struct cpuset *cs, char *buf)
  * cs:   the cpuset to update
  * buf:   the buffer where we read the 0 or 1
  *
- * Call with manage_mutex held.
+ * Call with cgroup_mutex held.
  */
 
 static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
@@ -1200,6 +1154,7 @@ static int fmeter_getrate(struct fmeter *fmp)
    return val;
 }
 
+/* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
 static int cpuset_can_attach(struct cgroup_subsys *ss,
               struct cgroup *cont, struct task_struct *tsk)
 {
@@ -1547,7 +1502,8 @@ static int cpuset_populate(struct cgroup_subsys *ss, struct cgroup *cont)
  * If this becomes a problem for some users who wish to
  * allow that scenario, then cpuset_post_clone() could be
  * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
- * (and likewise for mems) to the new cgroup.
+ * (and likewise for mems) to the new cgroup. Called with cgroup_mutex
+ * held.
  */
 static void cpuset_post_clone(struct cgroup_subsys *ss,
                struct cgroup *cgroup)
@@ -1571,11 +1527,8 @@ static void cpuset_post_clone(struct cgroup_subsys *ss,
 
 /*
  *   cpuset_create - create a cpuset
- *   parent:   cpuset that will be parent of the new cpuset.
- *   name:      name of the new cpuset. Will be strcpy'ed.
- *   mode:      mode to set on new inode
- *
- *   Must be called with the mutex on the parent inode held
+ *   ss:   cpuset cgroup subsystem
+ *   cont:   control group that the new cpuset will be part of
  */
 
 static struct cgroup_subsys_state *cpuset_create(
@@ -1617,10 +1570,10 @@ static struct cgroup_subsys_state *cpuset_create(
  *
  * If the cpuset being removed has its flag 'sched_load_balance'
  * enabled, then simulate turning sched_load_balance off, which
- * will call rebuild_sched_domains().  The lock_cpu_hotplug()
+ * will call rebuild_sched_domains().  The get_online_cpus()
  * call in rebuild_sched_domains() must not be made while holding
  * callback_mutex.  Elsewhere the kernel nests callback_mutex inside
- * lock_cpu_hotplug() calls.  So the reverse nesting would risk an
+ * get_online_cpus() calls.  So the reverse nesting would risk an
  * ABBA deadlock.
  */
 
@@ -1687,53 +1640,140 @@ int __init cpuset_init(void)
    return 0;
 }
 
+/**
+ * cpuset_do_move_task - move a given task to another cpuset
+ * @tsk: pointer to task_struct the task to move
+ * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
+ *
+ * Called by cgroup_scan_tasks() for each task in a cgroup.
+ * Return nonzero to stop the walk through the tasks.
+ */
+void cpuset_do_move_task(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+   struct cpuset_hotplug_scanner *chsp;
+
+   chsp = container_of(scan, struct cpuset_hotplug_scanner, scan);
+   cgroup_attach_task(chsp->to, tsk);
+}
+
+/**
+ * move_member_tasks_to_cpuset - move tasks from one cpuset to another
+ * @from: cpuset in which the tasks currently reside
+ * @to: cpuset to which the tasks will be moved
+ *
+ * Called with cgroup_mutex held
+ * callback_mutex must not be held, as cpuset_attach() will take it.
+ *
+ * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
+ * calling callback functions for each.
+ */
+static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
+{
+   struct cpuset_hotplug_scanner scan;
+
+   scan.scan.cg = from->css.cgroup;
+   scan.scan.test_task = NULL; /* select all tasks in cgroup */
+   scan.scan.process_task = cpuset_do_move_task;
+   scan.scan.heap = NULL;
+   scan.to = to->css.cgroup;
+
+   if (cgroup_scan_tasks((struct cgroup_scanner *)&scan))
+      printk(KERN_ERR "move_member_tasks_to_cpuset: "
+            "cgroup_scan_tasks failed\n");
+}
+
 /*
  * If common_cpu_mem_hotplug_unplug(), below, unplugs any CPUs
  * or memory nodes, we need to walk over the cpuset hierarchy,
  * removing that CPU or node from all cpusets.  If this removes the
- * last CPU or node from a cpuset, then the guarantee_online_cpus()
- * or guarantee_online_mems() code will use that emptied cpusets
- * parent online CPUs or nodes.  Cpusets that were already empty of
- * CPUs or nodes are left empty.
+ * last CPU or node from a cpuset, then move the tasks in the empty
+ * cpuset to its next-highest non-empty parent.
+ *
+ * Called with cgroup_mutex held
+ * callback_mutex must not be held, as cpuset_attach() will take it.
+ */
+static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
+{
+   struct cpuset *parent;
+
+   /*
+    * The cgroup's css_sets list is in use if there are tasks
+    * in the cpuset; the list is empty if there are none;
+    * the cs->css.refcnt seems always 0.
+    */
+   if (list_empty(&cs->css.cgroup->css_sets))
+      return;
+
+   /*
+    * Find its next-highest non-empty parent, (top cpuset
+    * has online cpus, so can't be empty).
+    */
+   parent = cs->parent;
+   while (cpus_empty(parent->cpus_allowed) ||
+         nodes_empty(parent->mems_allowed))
+      parent = parent->parent;
+
+   move_member_tasks_to_cpuset(cs, parent);
+}
+
+/*
+ * Walk the specified cpuset subtree and look for empty cpusets.
+ * The tasks of such cpuset must be moved to a parent cpuset.
  *
- * This routine is intentionally inefficient in a couple of regards.
- * It will check all cpusets in a subtree even if the top cpuset of
- * the subtree has no offline CPUs or nodes.  It checks both CPUs and
- * nodes, even though the caller could have been coded to know that
- * only one of CPUs or nodes needed to be checked on a given call.
- * This was done to minimize text size rather than cpu cycles.
+ * Called with cgroup_mutex held.  We take callback_mutex to modify
+ * cpus_allowed and mems_allowed.
  *
- * Call with both manage_mutex and callback_mutex held.
+ * This walk processes the tree from top to bottom, completing one layer
+ * before dropping down to the next.  It always processes a node before
+ * any of its children.
  *
- * Recursive, on depth of cpuset subtree.
+ * For now, since we lack memory hot unplug, we'll never see a cpuset
+ * that has tasks along with an empty 'mems'.  But if we did see such
+ * a cpuset, we'd handle it just like we do if its 'cpus' was empty.
  */
-
-static void guarantee_online_cpus_mems_in_subtree(const struct cpuset *cur)
+static void scan_for_empty_cpusets(const struct cpuset *root)
 {
+   struct cpuset *cp;   /* scans cpusets being updated */
+   struct cpuset *child;   /* scans child cpusets of cp */
+   struct list_head queue;
    struct cgroup *cont;
-   struct cpuset *c;
 
-   /* Each of our child cpusets mems must be online */
-   list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {
-      c = cgroup_cs(cont);
-      guarantee_online_cpus_mems_in_subtree(c);
-      if (!cpus_empty(c->cpus_allowed))
-         guarantee_online_cpus(c, &c->cpus_allowed);
-      if (!nodes_empty(c->mems_allowed))
-         guarantee_online_mems(c, &c->mems_allowed);
+   INIT_LIST_HEAD(&queue);
+
+   list_add_tail((struct list_head *)&root->stack_list, &queue);
+
+   while (!list_empty(&queue)) {
+      cp = container_of(queue.next, struct cpuset, stack_list);
+      list_del(queue.next);
+      list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
+         child = cgroup_cs(cont);
+         list_add_tail(&child->stack_list, &queue);
+      }
+      cont = cp->css.cgroup;
+
+      /* Continue past cpusets with all cpus, mems online */
+      if (cpus_subset(cp->cpus_allowed, cpu_online_map) &&
+          nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
+         continue;
+
+      /* Remove offline cpus and mems from this cpuset. */
+      mutex_lock(&callback_mutex);
+      cpus_and(cp->cpus_allowed, cp->cpus_allowed, cpu_online_map);
+      nodes_and(cp->mems_allowed, cp->mems_allowed,
+                  node_states[N_HIGH_MEMORY]);
+      mutex_unlock(&callback_mutex);
+
+      /* Move tasks from the empty cpuset to a parent */
+      if (cpus_empty(cp->cpus_allowed) ||
+           nodes_empty(cp->mems_allowed))
+         remove_tasks_in_empty_cpuset(cp);
    }
 }
 
 /*
  * The cpus_allowed and mems_allowed nodemasks in the top_cpuset track
  * cpu_online_map and node_states[N_HIGH_MEMORY].  Force the top cpuset to
- * track what's online after any CPU or memory node hotplug or unplug
- * event.
- *
- * To ensure that we don't remove a CPU or node from the top cpuset
- * that is currently in use by a child cpuset (which would violate
- * the rule that cpusets must be subsets of their parent), we first
- * call the recursive routine guarantee_online_cpus_mems_in_subtree().
+ * track what's online after any CPU or memory node hotplug or unplug event.
  *
  * Since there are two callers of this routine, one for CPU hotplug
  * events and one for memory node hotplug events, we could have coded
@@ -1744,13 +1784,11 @@ static void guarantee_online_cpus_mems_in_subtree(const struct cpuset *cur)
 static void common_cpu_mem_hotplug_unplug(void)
 {
    cgroup_lock();
-   mutex_lock(&callback_mutex);
 
-   guarantee_online_cpus_mems_in_subtree(&top_cpuset);
    top_cpuset.cpus_allowed = cpu_online_map;
    top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
+   scan_for_empty_cpusets(&top_cpuset);
 
-   mutex_unlock(&callback_mutex);
    cgroup_unlock();
 }
 
@@ -1826,7 +1864,7 @@ cpumask_t cpuset_cpus_allowed(struct task_struct *tsk)
 
 /**
  * cpuset_cpus_allowed_locked - return cpus_allowed mask from a tasks cpuset.
- * Must be  called with callback_mutex held.
+ * Must be called with callback_mutex held.
  **/
 cpumask_t cpuset_cpus_allowed_locked(struct task_struct *tsk)
 {
@@ -2163,10 +2201,8 @@ void __cpuset_memory_pressure_bump(void)
  *  - Used for /proc/<pid>/cpuset.
  *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
  *    doesn't really matter if tsk->cpuset changes after we read it,
- *    and we take manage_mutex, keeping attach_task() from changing it
- *    anyway.  No need to check that tsk->cpuset != NULL, thanks to
- *    the_top_cpuset_hack in cpuset_exit(), which sets an exiting tasks
- *    cpuset to top_cpuset.
+ *    and we take cgroup_mutex, keeping cpuset_attach() from changing it
+ *    anyway.
  */
 static int proc_cpuset_show(struct seq_file *m, void *unused_v)
 {
@@ -2219,13 +2255,14 @@ const struct file_operations proc_cpuset_operations = {
 #endif /* CONFIG_PROC_PID_CPUSET */
 
 /* Display task cpus_allowed, mems_allowed in /proc/<pid>/status file. */
-char *cpuset_task_status_allowed(struct task_struct *task, char *buffer)
-{
-   buffer += sprintf(buffer, "Cpus_allowed:\t");
-   buffer += cpumask_scnprintf(buffer, PAGE_SIZE, task->cpus_allowed);
-   buffer += sprintf(buffer, "\n");
-   buffer += sprintf(buffer, "Mems_allowed:\t");
-   buffer += nodemask_scnprintf(buffer, PAGE_SIZE, task->mems_allowed);
-   buffer += sprintf(buffer, "\n");
-   return buffer;
+void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
+{
+   seq_printf(m, "Cpus_allowed:\t");
+   m->count += cpumask_scnprintf(m->buf + m->count, m->size - m->count,
+               task->cpus_allowed);
+   seq_printf(m, "\n");
+   seq_printf(m, "Mems_allowed:\t");
+   m->count += nodemask_scnprintf(m->buf + m->count, m->size - m->count,
+               task->mems_allowed);
+   seq_printf(m, "\n");
 }