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Date: Tue, 6 Oct 2015 10:31:52 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Josh Triplett <josh@...htriplett.org> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() On Tue, Oct 06, 2015 at 10:21:28AM -0700, Josh Triplett wrote: > On Tue, Oct 06, 2015 at 09:13:45AM -0700, Paul E. McKenney wrote: > > This commit adds an rcu_pointer_handoff() that is intended to mark > > situations where a structure's protection transitions from RCU to some > > other mechanism (locking, reference counting, whatever). These markings > > should allow external tools to more easily spot bugs involving leaking > > pointers out of RCU read-side critical sections. > > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > Shouldn't this expect the __rcu address space on the pointer, and cast > away the __rcu with __force? I do not believe so, given that the __rcu was already removed by a preceding rcu_dereference(). Or am I missing something? Thanx, Paul > > include/linux/rcupdate.h | 22 ++++++++++++++++++++++ > > 1 file changed, 22 insertions(+) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 6c3ceceb6148..587eb057e2fa 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -813,6 +813,28 @@ static inline void rcu_preempt_sleep_check(void) > > #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) > > > > /** > > + * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism > > + * @p: The pointer to hand off > > + * > > + * This is simply an identity function, but it documents where a pointer > > + * is handed off from RCU to some other synchronization mechanism, for > > + * example, reference counting or locking. In C11, it would map to > > + * kill_dependency(). It could be used as follows: > > + * > > + * rcu_read_lock(); > > + * p = rcu_dereference(gp); > > + * long_lived = is_long_lived(p); > > + * if (long_lived) { > > + * if (!atomic_inc_not_zero(p->refcnt)) > > + * long_lived = false; > > + * else > > + * p = rcu_pointer_handoff(p); > > + * } > > + * rcu_read_unlock(); > > + */ > > +#define rcu_pointer_handoff(p) (p) > > + > > +/** > > * rcu_read_lock() - mark the beginning of an RCU read-side critical section > > * > > * When synchronize_rcu() is invoked on one CPU while other CPUs > > -- > > 2.5.2 > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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