all the readers who were traversing the list when we deleted the
element are finished. We use <function>call_rcu()</function> to
register a callback which will actually destroy the object once
- the readers are finished.
+ all pre-existing readers are finished. Alternatively,
+ <function>synchronize_rcu()</function> may be used to block until
+ all pre-existing are finished.
</para>
<para>
But how does Read Copy Update know when the readers are
- object_put(obj);
+ list_del_rcu(&obj->list);
cache_num--;
-+ call_rcu(&obj->rcu, cache_delete_rcu, obj);
++ call_rcu(&obj->rcu, cache_delete_rcu);
}
/* Must be holding cache_lock */
if (++cache_num > MAX_CACHE_SIZE) {
struct object *i, *outcast = NULL;
list_for_each_entry(i, &cache, list) {
-@@ -85,6 +94,7 @@
- obj->popularity = 0;
- atomic_set(&obj->refcnt, 1); /* The cache holds a reference */
- spin_lock_init(&obj->lock);
-+ INIT_RCU_HEAD(&obj->rcu);
-
- spin_lock_irqsave(&cache_lock, flags);
- __cache_add(obj);
@@ -104,12 +114,11 @@
struct object *cache_find(int id)
{
</sect1>
</chapter>
+ <chapter id="apiref">
+ <title>Mutex API reference</title>
+ !Iinclude/linux/mutex.h
+ !Ekernel/mutex.c
+ </chapter>
+
<chapter id="references">
<title>Further reading</title>
vhost_dev_cleanup(dev);
memory->nregions = 0;
- dev->memory = memory;
+ RCU_INIT_POINTER(dev->memory, memory);
return 0;
}
fput(dev->log_file);
dev->log_file = NULL;
/* No one will access memory at this point */
- kfree(dev->memory);
- dev->memory = NULL;
+ kfree(rcu_dereference_protected(dev->memory,
+ lockdep_is_held(&dev->mutex)));
+ RCU_INIT_POINTER(dev->memory, NULL);
if (dev->mm)
mmput(dev->mm);
dev->mm = NULL;
WARN_ON(!list_empty(&dev->work_list));
- kthread_stop(dev->worker);
+ if (dev->worker) {
+ kthread_stop(dev->worker);
+ dev->worker = NULL;
+ }
}
static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
/* Caller should have device mutex but not vq mutex */
int vhost_log_access_ok(struct vhost_dev *dev)
{
- return memory_access_ok(dev, dev->memory, 1);
+ struct vhost_memory *mp;
+
+ mp = rcu_dereference_protected(dev->memory,
+ lockdep_is_held(&dev->mutex));
+ return memory_access_ok(dev, mp, 1);
}
/* Verify access for write logging. */
/* Caller should have vq mutex and device mutex */
static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
{
- return vq_memory_access_ok(log_base, vq->dev->memory,
+ struct vhost_memory *mp;
+
+ mp = rcu_dereference_protected(vq->dev->memory,
+ lockdep_is_held(&vq->mutex));
+ return vq_memory_access_ok(log_base, mp,
vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
(!vq->log_used || log_access_ok(log_base, vq->log_addr,
sizeof *vq->used +
kfree(newmem);
return -EFAULT;
}
- oldmem = d->memory;
+ oldmem = rcu_dereference_protected(d->memory,
+ lockdep_is_held(&d->mutex));
rcu_assign_pointer(d->memory, newmem);
synchronize_rcu();
kfree(oldmem);
unsigned long flags;
/* ID for this css, if possible */
- struct css_id *id;
+ struct css_id __rcu *id;
};
/* bits in struct cgroup_subsys_state flags field */
struct list_head children; /* my children */
struct cgroup *parent; /* my parent */
- struct dentry *dentry; /* cgroup fs entry, RCU protected */
+ struct dentry __rcu *dentry; /* cgroup fs entry, RCU protected */
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
int cgroup_scan_tasks(struct cgroup_scanner *scan);
int cgroup_attach_task(struct cgroup *, struct task_struct *);
- int cgroup_attach_task_current_cg(struct task_struct *);
+ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+
+ static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+ {
+ return cgroup_attach_task_all(current, tsk);
+ }
/*
* CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
}
/* No cgroups - nothing to do */
+ static inline int cgroup_attach_task_all(struct task_struct *from,
+ struct task_struct *t)
+ {
+ return 0;
+ }
static inline int cgroup_attach_task_current_cg(struct task_struct *t)
{
return 0;
* is called after synchronize_rcu(). But for safe use, css_is_removed()
* css_tryget() should be used for avoiding race.
*/
- struct cgroup_subsys_state *css;
+ struct cgroup_subsys_state __rcu *css;
/*
* ID of this css.
*/
}
/**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
* @tsk: the task to be attached
*/
- int cgroup_attach_task_current_cg(struct task_struct *tsk)
+ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
{
struct cgroupfs_root *root;
- struct cgroup *cur_cg;
int retval = 0;
cgroup_lock();
for_each_active_root(root) {
- cur_cg = task_cgroup_from_root(current, root);
- retval = cgroup_attach_task(cur_cg, tsk);
+ struct cgroup *from_cg = task_cgroup_from_root(from, root);
+
+ retval = cgroup_attach_task(from_cg, tsk);
if (retval)
break;
}
return retval;
}
- EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+ EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
/*
* Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
/**
- * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
+ * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
*
* Check for bottom half being disabled, which covers both the
* CONFIG_PROVE_RCU and not cases. Note that if someone uses
* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
- * will show the situation.
+ * will show the situation. This is useful for debug checks in functions
+ * that require that they be called within an RCU read-side critical
+ * section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
*/
{
if (!debug_lockdep_rcu_enabled())
return 1;
- return in_softirq();
+ return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
unsigned int height; /* Height from the bottom */
unsigned int count;
struct rcu_head rcu_head;
- void *slots[RADIX_TREE_MAP_SIZE];
+ void __rcu *slots[RADIX_TREE_MAP_SIZE];
unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
};
{
struct radix_tree_node *node =
container_of(head, struct radix_tree_node, rcu_head);
+ int i;
/*
* must only free zeroed nodes into the slab. radix_tree_shrink
* can leave us with a non-NULL entry in the first slot, so clear
* that here to make sure.
*/
- tag_clear(node, 0, 0);
- tag_clear(node, 1, 0);
+ for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
+ tag_clear(node, i, 0);
+
node->slots[0] = NULL;
node->count = 0;
* also settag. The function stops either after tagging nr_to_tag items or
* after reaching last_index.
*
+ * The tags must be set from the leaf level only and propagated back up the
+ * path to the root. We must do this so that we resolve the full path before
+ * setting any tags on intermediate nodes. If we set tags as we descend, then
+ * we can get to the leaf node and find that the index that has the iftag
+ * set is outside the range we are scanning. This reults in dangling tags and
+ * can lead to problems with later tag operations (e.g. livelocks on lookups).
+ *
* The function returns number of leaves where the tag was set and sets
* *first_indexp to the first unscanned index.
* WARNING! *first_indexp can wrap if last_index is ULONG_MAX. Caller must
unsigned long nr_to_tag,
unsigned int iftag, unsigned int settag)
{
- unsigned int height = root->height, shift;
- unsigned long tagged = 0, index = *first_indexp;
- struct radix_tree_node *open_slots[height], *slot;
+ unsigned int height = root->height;
+ struct radix_tree_path path[height];
+ struct radix_tree_path *pathp = path;
+ struct radix_tree_node *slot;
+ unsigned int shift;
+ unsigned long tagged = 0;
+ unsigned long index = *first_indexp;
last_index = min(last_index, radix_tree_maxindex(height));
if (index > last_index)
shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
slot = radix_tree_indirect_to_ptr(root->rnode);
+ /*
+ * we fill the path from (root->height - 2) to 0, leaving the index at
+ * (root->height - 1) as a terminator. Zero the node in the terminator
+ * so that we can use this to end walk loops back up the path.
+ */
+ path[height - 1].node = NULL;
+
for (;;) {
int offset;
goto next;
if (!tag_get(slot, iftag, offset))
goto next;
+ if (height > 1) {
+ /* Go down one level */
+ height--;
+ shift -= RADIX_TREE_MAP_SHIFT;
+ path[height - 1].node = slot;
+ path[height - 1].offset = offset;
+ slot = slot->slots[offset];
+ continue;
+ }
+
+ /* tag the leaf */
+ tagged++;
tag_set(slot, settag, offset);
- if (height == 1) {
- tagged++;
- goto next;
+
+ /* walk back up the path tagging interior nodes */
+ pathp = &path[0];
+ while (pathp->node) {
+ /* stop if we find a node with the tag already set */
+ if (tag_get(pathp->node, settag, pathp->offset))
+ break;
+ tag_set(pathp->node, settag, pathp->offset);
+ pathp++;
}
- /* Go down one level */
- height--;
- shift -= RADIX_TREE_MAP_SHIFT;
- open_slots[height] = slot;
- slot = slot->slots[offset];
- continue;
+
next:
/* Go to next item at level determined by 'shift' */
index = ((index >> shift) + 1) << shift;
* last_index is guaranteed to be in the tree, what
* we do below cannot wander astray.
*/
- slot = open_slots[height];
+ slot = path[height - 1].node;
height++;
shift += RADIX_TREE_MAP_SHIFT;
}
git://bbs.cooldavid.org / net-next-2.6.git / commitdiff