This enables us to lookup a cgroup by its id.
v4:
- add a comment for idr_remove() in cgroup_offline_fn().
v3:
- on success, idr_alloc() returns the id but not 0, so fix the BUG_ON()
in cgroup_init().
- pass the right value to idr_alloc() so that the id for dummy cgroup is 0.
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
---
include/linux/cgroup.h | 4 ++--
kernel/cgroup.c | 33 +++++++++++++++++++++++++++------
2 files changed, 29 insertions(+), 8 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 297462b..2bd052d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -161,7 +161,7 @@ struct cgroup_name {
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */
- int id; /* ida allocated in-hierarchy ID */
+ int id; /* idr allocated in-hierarchy ID */
/*
* We link our 'sibling' struct into our parent's 'children'.
@@ -322,7 +322,7 @@ struct cgroupfs_root {
unsigned long flags;
/* IDs for cgroups in this hierarchy */
- struct ida cgroup_ida;
+ struct idr cgroup_idr;
/* The path to use for release notifications. */
char release_agent_path[PATH_MAX];
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 345fac8..a26e083 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -866,8 +866,6 @@ static void cgroup_free_fn(struct work_struct *work)
*/
dput(cgrp->parent->dentry);
- ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
-
/*
* Drop the active superblock reference that we took when we
* created the cgroup. This will free cgrp->root, if we are
@@ -1379,6 +1377,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
cgrp->root = root;
RCU_INIT_POINTER(cgrp->name, &root_cgroup_name);
init_cgroup_housekeeping(cgrp);
+ idr_init(&root->cgroup_idr);
}
static int cgroup_init_root_id(struct cgroupfs_root *root, int start, int end)
@@ -1451,7 +1450,6 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
*/
root->subsys_mask = opts->subsys_mask;
root->flags = opts->flags;
- ida_init(&root->cgroup_ida);
if (opts->release_agent)
strcpy(root->release_agent_path, opts->release_agent);
if (opts->name)
@@ -1467,7 +1465,7 @@ static void cgroup_free_root(struct cgroupfs_root *root)
/* hierarhcy ID shoulid already have been released */
WARN_ON_ONCE(root->hierarchy_id);
- ida_destroy(&root->cgroup_ida);
+ idr_destroy(&root->cgroup_idr);
kfree(root);
}
}
@@ -1582,6 +1580,11 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
mutex_lock(&cgroup_mutex);
mutex_lock(&cgroup_root_mutex);
+ root_cgrp->id = idr_alloc(&root->cgroup_idr, root_cgrp,
+ 0, 1, GFP_KERNEL);
+ if (root_cgrp->id < 0)
+ goto unlock_drop;
+
/* Check for name clashes with existing mounts */
ret = -EBUSY;
if (strlen(root->name))
@@ -4273,7 +4276,11 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
goto err_free_cgrp;
rcu_assign_pointer(cgrp->name, name);
- cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
+ /*
+ * Temporarily set the pointer to NULL, so idr_find() won't return
+ * a half-baked cgroup.
+ */
+ cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL);
if (cgrp->id < 0)
goto err_free_name;
@@ -4371,6 +4378,8 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
}
}
+ idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
+
err = cgroup_addrm_files(cgrp, NULL, cgroup_base_files, true);
if (err)
goto err_destroy;
@@ -4397,7 +4406,7 @@ err_free_all:
/* Release the reference count that we took on the superblock */
deactivate_super(sb);
err_free_id:
- ida_simple_remove(&root->cgroup_ida, cgrp->id);
+ idr_remove(&root->cgroup_idr, cgrp->id);
err_free_name:
kfree(rcu_dereference_raw(cgrp->name));
err_free_cgrp:
@@ -4590,6 +4599,14 @@ static void cgroup_offline_fn(struct work_struct *work)
/* delete this cgroup from parent->children */
list_del_rcu(&cgrp->sibling);
+ /*
+ * We should remove the cgroup object from idr before its grace
+ * period starts, so we won't be looking up a cgroup while the
+ * cgroup is being freed.
+ */
+ idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
+ cgrp->id = -1;
+
dput(d);
set_bit(CGRP_RELEASABLE, &parent->flags);
@@ -4915,6 +4932,10 @@ int __init cgroup_init(void)
BUG_ON(cgroup_init_root_id(&cgroup_dummy_root, 0, 1));
+ err = idr_alloc(&cgroup_dummy_root.cgroup_idr, cgroup_dummy_top,
+ 0, 1, GFP_KERNEL);
+ BUG_ON(err < 0);
+
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
--
1.8.0.2
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