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authorTejun Heo <tj@kernel.org>2015-09-16 13:03:02 -0400
committerTejun Heo <tj@kernel.org>2015-09-16 13:03:46 -0400
commit3014dde762f618fbcfe899f9ce9e929a2e5aa6dd (patch)
tree56e6df9207ba153da5cc9e6b989b00a40477dff1 /kernel/cgroup.c
parent1ed1328792ff46e4bb86a3d7f7be2971f4549f6c (diff)
downloadop-kernel-dev-3014dde762f618fbcfe899f9ce9e929a2e5aa6dd.zip
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cgroup: simplify threadgroup locking
Note: This commit was originally committed as b5ba75b5fc0e but got reverted by f9f9e7b77614 due to the performance regression from the percpu_rwsem write down/up operations added to cgroup task migration path. percpu_rwsem changes which alleviate the performance issue are pending for v4.4-rc1 merge window. Re-apply. Now that threadgroup locking is made global, code paths around it can be simplified. * lock-verify-unlock-retry dancing removed from __cgroup_procs_write(). * Race protection against de_thread() removed from cgroup_update_dfl_csses(). Signed-off-by: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c45
1 files changed, 12 insertions, 33 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 115091e..2cf0f79 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2460,14 +2460,13 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
if (!cgrp)
return -ENODEV;
-retry_find_task:
+ percpu_down_write(&cgroup_threadgroup_rwsem);
rcu_read_lock();
if (pid) {
tsk = find_task_by_vpid(pid);
if (!tsk) {
- rcu_read_unlock();
ret = -ESRCH;
- goto out_unlock_cgroup;
+ goto out_unlock_rcu;
}
} else {
tsk = current;
@@ -2483,37 +2482,23 @@ retry_find_task:
*/
if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
ret = -EINVAL;
- rcu_read_unlock();
- goto out_unlock_cgroup;
+ goto out_unlock_rcu;
}
get_task_struct(tsk);
rcu_read_unlock();
- percpu_down_write(&cgroup_threadgroup_rwsem);
- if (threadgroup) {
- if (!thread_group_leader(tsk)) {
- /*
- * a race with de_thread from another thread's exec()
- * may strip us of our leadership, if this happens,
- * there is no choice but to throw this task away and
- * try again; this is
- * "double-double-toil-and-trouble-check locking".
- */
- percpu_up_write(&cgroup_threadgroup_rwsem);
- put_task_struct(tsk);
- goto retry_find_task;
- }
- }
-
ret = cgroup_procs_write_permission(tsk, cgrp, of);
if (!ret)
ret = cgroup_attach_task(cgrp, tsk, threadgroup);
- percpu_up_write(&cgroup_threadgroup_rwsem);
-
put_task_struct(tsk);
-out_unlock_cgroup:
+ goto out_unlock_threadgroup;
+
+out_unlock_rcu:
+ rcu_read_unlock();
+out_unlock_threadgroup:
+ percpu_up_write(&cgroup_threadgroup_rwsem);
cgroup_kn_unlock(of->kn);
return ret ?: nbytes;
}
@@ -2658,6 +2643,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
lockdep_assert_held(&cgroup_mutex);
+ percpu_down_write(&cgroup_threadgroup_rwsem);
+
/* look up all csses currently attached to @cgrp's subtree */
down_read(&css_set_rwsem);
css_for_each_descendant_pre(css, cgroup_css(cgrp, NULL)) {
@@ -2713,17 +2700,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
goto out_finish;
last_task = task;
- percpu_down_write(&cgroup_threadgroup_rwsem);
- /* raced against de_thread() from another thread? */
- if (!thread_group_leader(task)) {
- percpu_up_write(&cgroup_threadgroup_rwsem);
- put_task_struct(task);
- continue;
- }
-
ret = cgroup_migrate(src_cset->dfl_cgrp, task, true);
- percpu_up_write(&cgroup_threadgroup_rwsem);
put_task_struct(task);
if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret))
@@ -2733,6 +2711,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
out_finish:
cgroup_migrate_finish(&preloaded_csets);
+ percpu_up_write(&cgroup_threadgroup_rwsem);
return ret;
}
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