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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 /kernel
parent9a3c4145af32125c5ee39c0272662b47307a8323 (diff)
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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 'kernel')
-rw-r--r--kernel/nsproxy.c15
-rw-r--r--kernel/utsname.c6
2 files changed, 7 insertions, 14 deletions
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 8e7811086b82..ef42d0ab3115 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -204,20 +204,13 @@ void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)
might_sleep();
+ task_lock(p);
ns = p->nsproxy;
+ p->nsproxy = new;
+ task_unlock(p);
- rcu_assign_pointer(p->nsproxy, new);
-
- if (ns && atomic_dec_and_test(&ns->count)) {
- /*
- * wait for others to get what they want from this nsproxy.
- *
- * cannot release this nsproxy via the call_rcu() since
- * put_mnt_ns() will want to sleep
- */
- synchronize_rcu();
+ if (ns && atomic_dec_and_test(&ns->count))
free_nsproxy(ns);
- }
}
void exit_task_namespaces(struct task_struct *p)
diff --git a/kernel/utsname.c b/kernel/utsname.c
index fd393124e507..883aaaa7de8a 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -93,13 +93,13 @@ static void *utsns_get(struct task_struct *task)
struct uts_namespace *ns = NULL;
struct nsproxy *nsproxy;
- rcu_read_lock();
- nsproxy = task_nsproxy(task);
+ task_lock(task);
+ nsproxy = task->nsproxy;
if (nsproxy) {
ns = nsproxy->uts_ns;
get_uts_ns(ns);
}
- rcu_read_unlock();
+ task_unlock(task);
return ns;
}