From 728dba3a39c66b3d8ac889ddbe38b5b1c264aec3 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 3 Feb 2014 19:13:49 -0800 Subject: 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 . 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" --- include/linux/nsproxy.h | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) (limited to 'include/linux/nsproxy.h') diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h index b4ec59d159a..35fa08fd773 100644 --- a/include/linux/nsproxy.h +++ b/include/linux/nsproxy.h @@ -40,32 +40,28 @@ extern struct nsproxy init_nsproxy; * the namespaces access rules are: * * 1. only current task is allowed to change tsk->nsproxy pointer or - * any pointer on the nsproxy itself + * any pointer on the nsproxy itself. Current must hold the task_lock + * when changing tsk->nsproxy. * * 2. when accessing (i.e. reading) current task's namespaces - no * precautions should be taken - just dereference the pointers * * 3. the access to other task namespaces is performed like this - * rcu_read_lock(); - * nsproxy = task_nsproxy(tsk); + * task_lock(task); + * nsproxy = task->nsproxy; * if (nsproxy != NULL) { * / * * * work with the namespaces here * * e.g. get the reference on one of them * * / * } / * - * * NULL task_nsproxy() means that this task is + * * NULL task->nsproxy means that this task is * * almost dead (zombie) * * / - * rcu_read_unlock(); + * task_unlock(task); * */ -static inline struct nsproxy *task_nsproxy(struct task_struct *tsk) -{ - return rcu_dereference(tsk->nsproxy); -} - int copy_namespaces(unsigned long flags, struct task_struct *tsk); void exit_task_namespaces(struct task_struct *tsk); void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new); -- cgit v1.2.3-70-g09d2