Messages in this thread | | | Date | Tue, 25 Aug 2009 18:31:36 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH -tip] Re: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU |
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On Wed, Aug 26, 2009 at 08:53:20AM +0800, Lai Jiangshan wrote: > Paul E. McKenney wrote: > > On Tue, Aug 25, 2009 at 02:02:33PM -0400, Mathieu Desnoyers wrote: > >> * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > >>> On Tue, Aug 25, 2009 at 12:25:49PM -0400, Mathieu Desnoyers wrote: > >>>> * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > >>>>> On Tue, Aug 25, 2009 at 10:00:47AM +0200, Ingo Molnar wrote: > >>>>>> btw., i'm still seeing crashes with the latest RCU bits: > >>>>>> > >>>>>> [ 20.621740] Testing event sys_enter_futex: OK > >>>>>> [ 20.629738] Testing event sys_exit_futex: OK > >>>>>> [ 20.637737] Testing event lock_acquire: [reboot] > >>>>>> > >>>>>> Possibly due to infinite recursion as well. Config attached. > >>>>> Color me confused... > >>>>> > >>>>> Unless someone has a better idea, I will send in a patch that adds > >>>>> "notrace" to every RCU API member used by any file in the kernel > >>>>> that has "trace" in its name (excluding ptrace.c and rcutree_trace.c, > >>>>> of course). This list is as follows: > >>>>> > >>>>> call_rcu() > >>>>> call_rcu_sched() > >>>>> rcu_read_lock() > >>>>> rcu_read_unlock() > >>>>> > >>>>> So, any better ideas? > >>>> Tracers using RCU should use the _notrace() version of read_lock/unlock. > >>>> I think the callers should be fixed rather than RCU. > >>>> > >>>> Tracepoints have been designed to use the _notrace variant on the > >>>> instrumentation site. The core of tracepoint management use > >>>> call_rcu_sched(), which can be traced without any problem. > >>>> > >>>> I have not followed the late tracing development as closely though, so > >>>> errors might have crept in. > >>> Or I might have inadvertently broken something in a non-obvious (to me, > >>> anyway) manner. > >>> > >>> So, would you be willing to look at commit bc33f24bd in the -tip > >>> tree and see if there is anything I broke other than the now-fixed > >>> rcu_read_lock_sched_notrace() and rcu_read_unlock_sched_notrace()? > >>> And for that matter, whether my alleged fix for these two API members > >>> really does fix the problem (-tip commit 7c614d6461)? > >>> > >>> The -tip tree is at: > >>> > >>> git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git > >>> > >>> And these patches are on the tip/core/rcu branch. > >>> > >> sure, here we go: > >> > >> static inline void rcu_read_lock_sched_notrace(void) > >> { > >> preempt_disable_notrace(); > >> + __acquire(RCU_SCHED); > >> + rcu_read_acquire(); > >> } > >> > >> and > >> > >> > >> static inline void rcu_read_unlock_sched_notrace(void) > >> { > >> + rcu_read_release(); > >> + __release(RCU_SCHED); > >> preempt_enable_notrace(); > >> } > >> > >> will make those _notrace primitives call into lockdep. I don't think > >> this is correct, and this might be causing your problem. > >> > >> rcu_read_acquire/release are calling lock_acquire/release, those should > >> be removed. > >> > >> __acquire() simply seems to be defined to a gcc "context" attribute, > >> probably for the sparse checker. I think it should be safe to leave them > >> there. > > > > Thank you for looking this over, Mathieu!!! Please see below for patch. > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > Remove lockdep annotations from RCU's _notrace() API members. > > > > The lockdep annotations rcu_read_acquire() and rcu_read_release() > > might lead to infinite looping if called from lockdep. So this patch > > removes them. > > > > Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > rcupdate.h | 2 -- > > 1 file changed, 2 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 8b4422c..95e0615 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -195,7 +195,6 @@ static inline notrace void rcu_read_lock_sched_notrace(void) > > { > > preempt_disable_notrace(); > > __acquire(RCU_SCHED); > > - rcu_read_acquire(); > > } > > > > /* > > @@ -211,7 +210,6 @@ static inline void rcu_read_unlock_sched(void) > > } > > static inline notrace void rcu_read_unlock_sched_notrace(void) > > { > > - rcu_read_release(); > > __release(RCU_SCHED); > > preempt_enable_notrace(); > > } > > I remembered I have suggested this ...
Ah!!! I understood the "add notrace" suggestion, but was confused into thinking that "notrace" was going to prevent it from being called the second time.
> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Thank you!!!
Thanx, Paul
> Lai Jiangshan wrote: > > > >> { > >> preempt_disable_notrace(); > >> + __acquire(RCU_SCHED); > >> + rcu_read_acquire(); > >> } > >> > > > > It may cause infinity recursion. > > rcu_read_acquire() calls rcu_read_lock_sched_notrace() > > before current->lockdep_recursion is set to 1 when tracing in on, > > thus infinity recursion occurs. > > > > Lai > > > >
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