cgroup: protect cgroup_root->cgroup_idr with a spinlock
Currently, cgroup_root->cgroup_idr is protected by cgroup_mutex, which
ends up requiring cgroup_put() to be invoked under sleepable context.
This is okay for now but is an unusual requirement and we'll soon add
css->id which will have the same problem but won't be able to simply
grab cgroup_mutex as removal will have to happen from css_release()
which can't sleep.
Introduce cgroup_idr_lock and idr_alloc/replace/remove() wrappers
which protects the idr operations with the lock and use them for
cgroup_root->cgroup_idr. cgroup_put() no longer needs to grab
cgroup_mutex and css_from_id() is updated to always require RCU read
lock instead of either RCU read lock or cgroup_mutex, which doesn't
affect the existing users.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3fa0463..7cb9c08 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -100,6 +100,12 @@
#endif
/*
+ * Protects cgroup_idr so that IDs can be released without grabbing
+ * cgroup_mutex.
+ */
+static DEFINE_SPINLOCK(cgroup_idr_lock);
+
+/*
* Protects cgroup_subsys->release_agent_path. Modifying it also requires
* cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
*/
@@ -190,6 +196,37 @@
bool is_add);
static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);
+/* IDR wrappers which synchronize using cgroup_idr_lock */
+static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
+ gfp_t gfp_mask)
+{
+ int ret;
+
+ idr_preload(gfp_mask);
+ spin_lock(&cgroup_idr_lock);
+ ret = idr_alloc(idr, ptr, start, end, gfp_mask);
+ spin_unlock(&cgroup_idr_lock);
+ idr_preload_end();
+ return ret;
+}
+
+static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
+{
+ void *ret;
+
+ spin_lock(&cgroup_idr_lock);
+ ret = idr_replace(idr, ptr, id);
+ spin_unlock(&cgroup_idr_lock);
+ return ret;
+}
+
+static void cgroup_idr_remove(struct idr *idr, int id)
+{
+ spin_lock(&cgroup_idr_lock);
+ idr_remove(idr, id);
+ spin_unlock(&cgroup_idr_lock);
+}
+
/**
* cgroup_css - obtain a cgroup's css for the specified subsystem
* @cgrp: the cgroup of interest
@@ -1058,9 +1095,7 @@
* per-subsystem and moved to css->id so that lookups are
* successful until the target css is released.
*/
- mutex_lock(&cgroup_mutex);
- idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
- mutex_unlock(&cgroup_mutex);
+ cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
cgrp->id = -1;
call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
@@ -1531,7 +1566,7 @@
lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
- ret = idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
+ ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);
if (ret < 0)
goto out;
root_cgrp->id = ret;
@@ -4225,7 +4260,7 @@
* Temporarily set the pointer to NULL, so idr_find() won't return
* a half-baked cgroup.
*/
- cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
+ cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_NOWAIT);
if (cgrp->id < 0) {
err = -ENOMEM;
goto err_unlock;
@@ -4268,7 +4303,7 @@
* @cgrp is now fully operational. If something fails after this
* point, it'll be released via the normal destruction path.
*/
- idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
+ cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
err = cgroup_kn_set_ugid(kn);
if (err)
@@ -4302,7 +4337,7 @@
return 0;
err_free_id:
- idr_remove(&root->cgroup_idr, cgrp->id);
+ cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
err_unlock:
mutex_unlock(&cgroup_mutex);
err_unlock_tree:
@@ -5162,7 +5197,7 @@
{
struct cgroup *cgrp;
- cgroup_assert_mutexes_or_rcu_locked();
+ WARN_ON_ONCE(!rcu_read_lock_held());
cgrp = idr_find(&ss->root->cgroup_idr, id);
if (cgrp)
