Messages in this thread | | | Date | Fri, 25 Jun 2010 10:48:12 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 2.6.35-rc3] Add RCU check for find_task_by_vpid(). |
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On Sat, Jun 26, 2010 at 01:08:19AM +0900, Tetsuo Handa wrote: > find_task_by_vpid() says "Must be called under rcu_read_lock().". But due to > commit 3120438 "rcu: Disable lockdep checking in RCU list-traversal primitives", > we are currently unable to catch "find_task_by_vpid() with tasklist_lock held > but RCU lock not held" errors. > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/pid.c:386 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by rc.sysinit/1102: > #0: (tasklist_lock){.+.+..}, at: [<c1048340>] sys_setpgid+0x40/0x160 > > stack backtrace: > Pid: 1102, comm: rc.sysinit Not tainted 2.6.35-rc3-dirty #1 > Call Trace: > [<c105e714>] lockdep_rcu_dereference+0x94/0xb0 > [<c104b4cd>] find_task_by_pid_ns+0x6d/0x70 > [<c104b4e8>] find_task_by_vpid+0x18/0x20 > [<c1048347>] sys_setpgid+0x47/0x160 > [<c1002b50>] sysenter_do_call+0x12/0x36 > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > --- > diff --git a/kernel/pid.c b/kernel/pid.c > index e9fd8c1..a257471 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -382,6 +382,9 @@ EXPORT_SYMBOL(pid_task); > */ > struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) > { > +#ifdef __do_rcu_dereference_check > + __do_rcu_dereference_check(rcu_read_lock_held()); > +#endif
How about the following?
WARN_ON_ONCE(!rcu_read_lock_held());
> return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); > } >
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