The patch titled
cgroups: make cgroup_path() RCU-safe
has been added to the -mm tree. Its filename is
cgroups-make-cgroup_path-rcu-safe.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: cgroups: make cgroup_path() RCU-safe
From: Paul Menage <menage@xxxxxxxxxx>
Fix races between /proc/sched_debug by freeing cgroup objects via an RCU
callback. Thus any cgroup reference obtained from an RCU-safe source will
remain valid during the RCU section. Since dentries are also RCU-safe,
this allows us to traverse up the tree safely.
Additionally, make cgroup_path() check for a NULL cgrp->dentry to avoid
trying to report a path for a partially-created cgroup.
Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
Reviewed-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
Tested-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 11 ++++++++++-
kernel/cgroup.c | 33 ++++++++++++++++++++++-----------
2 files changed, 32 insertions(+), 12 deletions(-)
diff -puN include/linux/cgroup.h~cgroups-make-cgroup_path-rcu-safe include/linux/cgroup.h
--- a/include/linux/cgroup.h~cgroups-make-cgroup_path-rcu-safe
+++ a/include/linux/cgroup.h
@@ -116,7 +116,7 @@ struct cgroup {
struct list_head children; /* my children */
struct cgroup *parent; /* my parent */
- struct dentry *dentry; /* cgroup fs entry */
+ struct dentry *dentry; /* cgroup fs entry, RCU protected */
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
@@ -145,6 +145,9 @@ struct cgroup {
int pids_use_count;
/* Length of the current tasks_pids array */
int pids_length;
+
+ /* For RCU-protected deletion */
+ struct rcu_head rcu_head;
};
/* A css_set is a structure holding pointers to a set of
@@ -305,6 +308,12 @@ int cgroup_add_files(struct cgroup *cgrp
int cgroup_is_removed(const struct cgroup *cgrp);
+/*
+ * cgroup_path() fills in a filesystem-like path for the given cgroup
+ * into "buf", up to "buflen" characters. Should be called with
+ * cgroup_mutex held, or else in an RCU section with an RCU-protected
+ * cgroup reference
+ */
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
int cgroup_task_count(const struct cgroup *cgrp);
diff -puN kernel/cgroup.c~cgroups-make-cgroup_path-rcu-safe kernel/cgroup.c
--- a/kernel/cgroup.c~cgroups-make-cgroup_path-rcu-safe
+++ a/kernel/cgroup.c
@@ -271,7 +271,7 @@ static void __put_css_set(struct css_set
rcu_read_lock();
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- struct cgroup *cgrp = cg->subsys[i]->cgroup;
+ struct cgroup *cgrp = rcu_dereference(cg->subsys[i]->cgroup);
if (atomic_dec_and_test(&cgrp->count) &&
notify_on_release(cgrp)) {
if (taskexit)
@@ -595,6 +595,18 @@ static void cgroup_call_pre_destroy(stru
return;
}
+static void free_cgroup_rcu(struct rcu_head *obj)
+{
+ struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);
+ /*
+ * Drop the active superblock reference that we took when we
+ * created the cgroup
+ */
+ deactivate_super(cgrp->root->sb);
+
+ kfree(cgrp);
+}
+
static void cgroup_diput(struct dentry *dentry, struct inode *inode)
{
/* is dentry a directory ? if so, kfree() associated cgroup */
@@ -620,11 +632,7 @@ static void cgroup_diput(struct dentry *
cgrp->root->number_of_cgroups--;
mutex_unlock(&cgroup_mutex);
- /* Drop the active superblock reference that we took when we
- * created the cgroup */
- deactivate_super(cgrp->root->sb);
-
- kfree(cgrp);
+ call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
}
iput(inode);
}
@@ -1134,14 +1142,16 @@ static inline struct cftype *__d_cft(str
* @buf: the buffer to write the path into
* @buflen: the length of the buffer
*
- * Called with cgroup_mutex held. Writes path of cgroup into buf.
- * Returns 0 on success, -errno on error.
+ * Called with cgroup_mutex held or else with an RCU-protected cgroup
+ * reference. Writes path of cgroup into buf. Returns 0 on success,
+ * -errno on error.
*/
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
{
char *start;
+ struct dentry *dentry = rcu_dereference(cgrp->dentry);
- if (cgrp == dummytop) {
+ if (!dentry || cgrp == dummytop) {
/*
* Inactive subsystems have no dentry for their root
* cgroup
@@ -1154,13 +1164,14 @@ int cgroup_path(const struct cgroup *cgr
*--start = '\0';
for (;;) {
- int len = cgrp->dentry->d_name.len;
+ int len = dentry->d_name.len;
if ((start -= len) < buf)
return -ENAMETOOLONG;
memcpy(start, cgrp->dentry->d_name.name, len);
cgrp = cgrp->parent;
if (!cgrp)
break;
+ dentry = rcu_dereference(cgrp->dentry);
if (!cgrp->parent)
continue;
if (--start < buf)
@@ -1663,7 +1674,7 @@ static int cgroup_create_dir(struct cgro
if (!error) {
dentry->d_fsdata = cgrp;
inc_nlink(parent->d_inode);
- cgrp->dentry = dentry;
+ rcu_assign_pointer(cgrp->dentry, dentry);
dget(dentry);
}
dput(dentry);
_
Patches currently in -mm which might be from menage@xxxxxxxxxx are
origin.patch
linux-next.patch
cpuacct-refactoring-cpuusage_read-cpuusage_write.patch
cpuacct-export-percpu-cpuacct-cgroup-stats.patch
oom-print-triggering-tasks-cpuset-and-mems-allowed.patch
oom-print-triggering-tasks-cpuset-and-mems-allowed-fix.patch
mm-remove-cgroup_mm_owner_callbacks.patch
mm-make-get_user_pages-interruptible.patch
mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock.patch
cgroups-make-cgroup-config-a-submenu.patch
cgroups-documentation-updates.patch
cgroups-remove-some-redundant-null-checks.patch
ns_cgroup-remove-unused-spinlock.patch
memcg-fix-a-typo-in-kconfig.patch
cgroups-add-lock-for-child-cgroups-in-cgroup_post_fork.patch
cgroups-fix-cgroup_iter_next-bug.patch
cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu.patch
cgroups-use-task_lock-for-access-tsk-cgroups-safe-in-cgroup_clone.patch
cgroups-call-find_css_set-safely-in-cgroup_attach_task.patch
cgroups-remove-rcu_read_lock-in-cgroupstats_build.patch
cgroups-make-root_list-contains-active-hierarchies-only.patch
cgroups-add-inactive-subsystems-to-rootnodesubsys_list.patch
cgroups-add-inactive-subsystems-to-rootnodesubsys_list-fix.patch
cgroups-introduce-link_css_set-to-remove-duplicate-code.patch
cgroups-introduce-link_css_set-to-remove-duplicate-code-fix.patch
cgroups-skip-processes-from-other-namespaces-when-listing-a-cgroup.patch
cgroups-skip-processes-from-other-namespaces-when-listing-a-cgroup-checkpatch-fixes.patch
cgroups-make-cgroup_path-rcu-safe.patch
devcgroup-use-list_for_each_entry_rcu.patch
devices-cgroup-allow-mkfifo.patch
memcg-move-all-acccounts-to-parent-at-rmdir.patch
memory-cgroup-hierarchy-documentation-v4.patch
memory-cgroup-resource-counters-for-hierarchy-v4.patch
memory-cgroup-resource-counters-for-hierarchy-v4-checkpatch-fixes.patch
memory-cgroup-hierarchical-reclaim-v4.patch
memory-cgroup-hierarchical-reclaim-v4-checkpatch-fixes.patch
memory-cgroup-hierarchical-reclaim-v4-fix-for-hierarchical-reclaim.patch
memory-cgroup-hierarchy-feature-selector-v4.patch
memory-cgroup-hierarchy-feature-selector-v4-fix.patch
memcontrol-rcu_read_lock-to-protect-mm_match_cgroup.patch
cgroups-add-a-per-subsystem-hierarchy_mutex.patch
cgroups-use-hierarchy_mutex-in-memory-controller.patch
cgroups-add-css_tryget.patch
cpuset-rcu_read_lock-to-protect-task_cs.patch
add-a-refcount-check-in-dput.patch
--
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