path: root/ipc
diff options
authorEric W. Biederman <ebiederm@xmission.com>2014-02-03 19:13:49 -0800
committerEric W. Biederman <ebiederm@xmission.com>2014-07-29 18:08:50 -0700
commit728dba3a39c66b3d8ac889ddbe38b5b1c264aec3 (patch)
tree26f69d0fe363f00b628d698b9df2634a33e42482 /ipc
parent9a3c4145af32125c5ee39c0272662b47307a8323 (diff)
namespaces: Use task_lock and not rcu to protect nsproxy
The synchronous syncrhonize_rcu in switch_task_namespaces makes setns a sufficiently expensive system call that people have complained. Upon inspect nsproxy no longer needs rcu protection for remote reads. remote reads are rare. So optimize for same process reads and write by switching using rask_lock instead. This yields a simpler to understand lock, and a faster setns system call. In particular this fixes a performance regression observed by Rafael David Tinoco <rafael.tinoco@canonical.com>. This is effectively a revert of Pavel Emelyanov's commit cf7b708c8d1d7a27736771bcf4c457b332b0f818 Make access to task's nsproxy lighter from 2007. The race this originialy fixed no longer exists as do_notify_parent uses task_active_pid_ns(parent) instead of parent->nsproxy. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'ipc')
1 files changed, 3 insertions, 3 deletions
diff --git a/ipc/namespace.c b/ipc/namespace.c
index 59451c1e214d..b54468e48e32 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -154,11 +154,11 @@ static void *ipcns_get(struct task_struct *task)
struct ipc_namespace *ns = NULL;
struct nsproxy *nsproxy;
- rcu_read_lock();
- nsproxy = task_nsproxy(task);
+ task_lock(task);
+ nsproxy = task->nsproxy;
if (nsproxy)
ns = get_ipc_ns(nsproxy->ipc_ns);
- rcu_read_unlock();
+ task_unlock(task);
return ns;

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