Messages in this thread | | | Subject | Re: [RFC][PATCH 2/5] pid: Generalize task_active_pid_ns | From | Nadia Derbey <> | Date | Thu, 27 Nov 2008 14:09:31 +0100 |
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On Tue, 2008-11-25 at 19:45 -0800, Sukadev Bhattiprolu wrote: > >From 7f7caaa9d9014d7230dc0b1e0f75536f0b6ccdbf Mon Sep 17 00:00:00 2001 > From: Eric W. Biederman <ebiederm@xmission.com> > Date: Mon, 10 Nov 2008 19:12:02 -0800 > Subject: [PATCH 2/5] pid: Generalize task_active_pid_ns > > Currently task_active_pid_ns is not safe to call after a > task becomes a zombie and exit_task_namespaces is called, > as nsproxy becomes NULL. By reading the pid namespace from > the pid of the task we can trivially solve this problem at > the cost of one extra memory read in what should be the > same cacheline as we read the namespace from. > > When moving things around I have made task_active_pid_ns > out of line because keeping it in pid_namespace.h would > require adding includes of pid.h and sched.h that I > don't think we want. > > This change does make task_active_pid_ns unsafe to call during > copy_process until we attach a pid on the task_struct which > seems to be a reasonable trade off. > > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > --- > include/linux/pid_namespace.h | 6 +----- > kernel/fork.c | 4 ++-- > kernel/pid.c | 6 ++++++ > 3 files changed, 9 insertions(+), 7 deletions(-) > > diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h > index d82fe82..38d1032 100644 > --- a/include/linux/pid_namespace.h > +++ b/include/linux/pid_namespace.h > @@ -79,11 +79,7 @@ static inline void zap_pid_ns_processes(struct pid_namespace *ns) > } > #endif /* CONFIG_PID_NS */ > > -static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) > -{ > - return tsk->nsproxy->pid_ns; > -} > - > +extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk); > void pidhash_init(void); > void pidmap_init(void); > > diff --git a/kernel/fork.c b/kernel/fork.c > index f608356..28be39a 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1111,12 +1111,12 @@ static struct task_struct *copy_process(unsigned long clone_flags, >
Suka,
I'm wondering if it is still safe to keep the call to task_active_pid_ns() in create_new_namespaces(): copy_namespaces() is called a couple of lines above this sequence and it calls create_new_namespaces(). So I don't see why you're now referencing p->nsproxy->pid_ns here and not in create_new_namespaces()?
Regards, Nadia
> if (pid != &init_struct_pid) { > retval = -ENOMEM; > - pid = alloc_pid(task_active_pid_ns(p)); > + pid = alloc_pid(p->nsproxy->pid_ns); > if (!pid) > goto bad_fork_cleanup_io; > > if (clone_flags & CLONE_NEWPID) { > - retval = pid_ns_prepare_proc(task_active_pid_ns(p)); > + retval = pid_ns_prepare_proc(p->nsproxy->pid_ns); > if (retval < 0) > goto bad_fork_free_pid; > } > diff --git a/kernel/pid.c b/kernel/pid.c > index 064e76a..c5513fe 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -474,6 +474,12 @@ pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) > } > EXPORT_SYMBOL(task_session_nr_ns); > > +struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) > +{ > + return ns_of_pid(task_pid(tsk)); > +} > +EXPORT_SYMBOL_GPL(task_active_pid_ns); > + > /* > * Used by proc to find the first pid that is greater then or equal to nr. > * -- Nadia Derbey <Nadia.Derbey@bull.net>
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