Messages in this thread | | | Date | Wed, 10 Feb 2010 12:30:50 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] Update comment on find_task_by_pid_ns |
| |
On Wed, Feb 10, 2010 at 02:18:34PM -0600, Serge E. Hallyn wrote: > Quoting Thomas Gleixner (tglx@linutronix.de): > > On Wed, 10 Feb 2010, Andrew Morton wrote: > > > On Wed, 10 Feb 2010 10:30:33 -0600 "Serge E. Hallyn" <serue@us.ibm.com> wrote: > > > > > > > Quoting Andrew Morton (akpm@linux-foundation.org): > > > > > On Tue, 9 Feb 2010 06:42:45 +0900 > > > > > Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote: > > > > > > > > > > > OK. I updated description. > > > > > > > > > > > > As of 2.6.32 , below users are missing rcu_read_lock(). > > > > > > > > > > > > Users missing rcu_read_lock() when calling find_task_by_vpid(): > > > > > > > > > > > > SYSCALL_DEFINE3(ioprio_set) in fs/ioprio.c > > > > > > SYSCALL_DEFINE2(ioprio_get) in fs/ioprio.c > > > > > > cap_get_target_pid() in kernel/capability.c > > > > > > > > > > Actually, cap_get_target_pid() uses rcu_read_lock() and doesn't take > > > > > tasklist_lock. > > > > > > > > Hmm - is that in -mm? In my copy here it takes read_lock(&tasklist_lock) > > > > > > yup. It got changed in linux-next. > > > > > > > And I'll admit I'm a bit confused as to the current state of things: > > > > do I understand correctly that we now need to take both the tasklist_lock > > > > and rcu_read_lock? (Presumably only for read_lock()?) > > > > > > Beats me. We need to protect both the pid->task_struct lookup data > > > structures (during the lookup) and protect the resulting task_struct > > > while the caller is playing with it. It's unclear whether > > > rcu_read_lock() suffices for both purposes. > > > > The rcu_read_lock section is sufficient. task_struct can not go away > > before the rcu_read_unlock() > > But, more generally, it used to be the case that a spinlock (or > rwlock) would imply an rcu read cycle, but now it no longer does, > do I understand that right?
You are correct, with CONFIG_PREEMPT_RCU, acquiring a lock does -not- imply an RCU read-side critical section. And acquiring a lock does -not- imply any sort of RCU read-side critical section in -rt kernels in any case.
Thanx, Paul
| |