Messages in this thread | | | Date | Tue, 25 Aug 2009 14:02:33 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU |
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* 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.
Mathieu
> Thanx, Paul
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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