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https://github.com/torvalds/linux
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728dba3a39
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
cf7b708c8d 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>
140 lines
2.9 KiB
C
140 lines
2.9 KiB
C
/*
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* Copyright (C) 2004 IBM Corporation
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*
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* Author: Serge Hallyn <serue@us.ibm.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation, version 2 of the
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* License.
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*/
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#include <linux/export.h>
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#include <linux/uts.h>
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#include <linux/utsname.h>
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#include <linux/err.h>
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#include <linux/slab.h>
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#include <linux/user_namespace.h>
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#include <linux/proc_ns.h>
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static struct uts_namespace *create_uts_ns(void)
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{
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struct uts_namespace *uts_ns;
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uts_ns = kmalloc(sizeof(struct uts_namespace), GFP_KERNEL);
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if (uts_ns)
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kref_init(&uts_ns->kref);
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return uts_ns;
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}
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/*
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* Clone a new ns copying an original utsname, setting refcount to 1
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* @old_ns: namespace to clone
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* Return ERR_PTR(-ENOMEM) on error (failure to kmalloc), new ns otherwise
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*/
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static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
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struct uts_namespace *old_ns)
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{
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struct uts_namespace *ns;
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int err;
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ns = create_uts_ns();
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if (!ns)
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return ERR_PTR(-ENOMEM);
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err = proc_alloc_inum(&ns->proc_inum);
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if (err) {
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kfree(ns);
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return ERR_PTR(err);
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}
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down_read(&uts_sem);
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memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
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ns->user_ns = get_user_ns(user_ns);
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up_read(&uts_sem);
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return ns;
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}
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/*
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* Copy task tsk's utsname namespace, or clone it if flags
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* specifies CLONE_NEWUTS. In latter case, changes to the
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* utsname of this process won't be seen by parent, and vice
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* versa.
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*/
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struct uts_namespace *copy_utsname(unsigned long flags,
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struct user_namespace *user_ns, struct uts_namespace *old_ns)
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{
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struct uts_namespace *new_ns;
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BUG_ON(!old_ns);
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get_uts_ns(old_ns);
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if (!(flags & CLONE_NEWUTS))
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return old_ns;
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new_ns = clone_uts_ns(user_ns, old_ns);
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put_uts_ns(old_ns);
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return new_ns;
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}
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void free_uts_ns(struct kref *kref)
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{
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struct uts_namespace *ns;
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ns = container_of(kref, struct uts_namespace, kref);
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put_user_ns(ns->user_ns);
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proc_free_inum(ns->proc_inum);
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kfree(ns);
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}
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static void *utsns_get(struct task_struct *task)
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{
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struct uts_namespace *ns = NULL;
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struct nsproxy *nsproxy;
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task_lock(task);
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nsproxy = task->nsproxy;
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if (nsproxy) {
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ns = nsproxy->uts_ns;
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get_uts_ns(ns);
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}
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task_unlock(task);
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return ns;
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}
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static void utsns_put(void *ns)
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{
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put_uts_ns(ns);
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}
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static int utsns_install(struct nsproxy *nsproxy, void *new)
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{
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struct uts_namespace *ns = new;
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if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
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!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
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return -EPERM;
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get_uts_ns(ns);
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put_uts_ns(nsproxy->uts_ns);
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nsproxy->uts_ns = ns;
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return 0;
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}
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static unsigned int utsns_inum(void *vp)
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{
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struct uts_namespace *ns = vp;
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return ns->proc_inum;
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}
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const struct proc_ns_operations utsns_operations = {
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.name = "uts",
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.type = CLONE_NEWUTS,
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.get = utsns_get,
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.put = utsns_put,
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.install = utsns_install,
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.inum = utsns_inum,
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};
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