On Mon, 27 Oct 2014, Paul E. McKenney wrote: > On Mon, Oct 27, 2014 at 08:10:21AM -0700, Paul E. McKenney wrote: > > On Mon, Oct 27, 2014 at 09:47:57AM -0400, Eric B Munson wrote: > > > On Fri, 24 Oct 2014, Paul E. McKenney wrote: > > [ . . . ] > > > > > > Still didn't help. If it helps, when I attempt to reboot after trying > > > > > to hibernate I see a kworker thread hung and get the stack trace below > > > > > from that thread. I assume this is the same thread that is holding up > > > > > the hibernate. > > > > > > > > Yep, looks like something that some other people are running into as > > > > well. > > > > > > > > If you turn off CONFIG_RCU_NOCB_CPU, do you still get the failure? > > > > > > Disabling CONFIG_RCU_NOCB_CPU fixes the problem. I am able to hibernate > > > and resume successfully. > > > > Very good! Then the fix I am working on might actually be a fix. ;-) > > And here is a patch that passes preliminary testing at my end. Does it > help at your end? > > Thanx, Paul
Thanks Paul, that fixed it for me. Feel free to add my Tested-by: to the patch. Eric > > ------------------------------------------------------------------------ > > rcu: Make rcu_barrier() understand about missing rcuo kthreads > > Commit 35ce7f29a44a (rcu: Create rcuo kthreads only for onlined CPUs) > avoids creating rcuo kthreads for CPUs that never come online. This > fixes a bug in many instances of firmware: Instead of lying about their > age, these systems instead lie about the number of CPUs that they have. > Before commit 35ce7f29a44a, this could result in huge numbers of useless > rcuo kthreads being created. > > It appears that experience indicates that I should have told the > people suffering from this problem to fix their broken firmware, but > I instead produced what turned out to be a partial fix. The missing > piece supplied by this commit makes sure that rcu_barrier() knows not to > post callbacks for no-CBs CPUs that have not yet come online, because > otherwise rcu_barrier() will hang on systems having firmware that lies > about the number of CPUs. > > It is tempting to simply have rcu_barrier() refuse to post a callback on > any no-CBs CPU that does not have an rcuo kthread. This unfortunately > does not work because rcu_barrier() is required to wait for all pending > callbacks. It is therefore required to wait even for those callbacks > that cannot possibly be invoked. Even if doing so hangs the system. > > Given that posting a callback to a no-CBs CPU that does not yet have an > rcuo kthread can hang rcu_barrier(), It is tempting to report an error > in this case. Unfortunately, this will result in false positives at > boot time, when it is perfectly legal to post callbacks to the boot CPU > before the scheduler has started, in other words, before it is legal > to invoke rcu_barrier(). > > So this commit instead has rcu_barrier() avoid posting callbacks to > CPUs having neither rcuo kthread nor pending callbacks, and has it > complain bitterly if it finds CPUs having no rcuo kthread but some > pending callbacks. And when rcu_barrier() does find CPUs having no rcuo > kthread but pending callbacks, as noted earlier, it has no choice but > to hang indefinitely. > > Reported-by: Yanko Kaneti <[email protected]> > Reported-by: Jay Vosburgh <[email protected]> > Reported-by: Eric B Munson <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h > index aa8e5eea3ab4..c78e88ce5ea3 100644 > --- a/include/trace/events/rcu.h > +++ b/include/trace/events/rcu.h > @@ -660,18 +660,18 @@ TRACE_EVENT(rcu_torture_read, > /* > * Tracepoint for _rcu_barrier() execution. The string "s" describes > * the _rcu_barrier phase: > - * "Begin": rcu_barrier_callback() started. > - * "Check": rcu_barrier_callback() checking for piggybacking. > - * "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit. > - * "Inc1": rcu_barrier_callback() piggyback check counter incremented. > - * "Offline": rcu_barrier_callback() found offline CPU > - * "OnlineNoCB": rcu_barrier_callback() found online no-CBs CPU. > - * "OnlineQ": rcu_barrier_callback() found online CPU with callbacks. > - * "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks. > + * "Begin": _rcu_barrier() started. > + * "Check": _rcu_barrier() checking for piggybacking. > + * "EarlyExit": _rcu_barrier() piggybacked, thus early exit. > + * "Inc1": _rcu_barrier() piggyback check counter incremented. > + * "OfflineNoCB": _rcu_barrier() found callback on never-online CPU > + * "OnlineNoCB": _rcu_barrier() found online no-CBs CPU. > + * "OnlineQ": _rcu_barrier() found online CPU with callbacks. > + * "OnlineNQ": _rcu_barrier() found online CPU, no callbacks. > * "IRQ": An rcu_barrier_callback() callback posted on remote CPU. > * "CB": An rcu_barrier_callback() invoked a callback, not the last. > * "LastCB": An rcu_barrier_callback() invoked the last callback. > - * "Inc2": rcu_barrier_callback() piggyback check counter incremented. > + * "Inc2": _rcu_barrier() piggyback check counter incremented. > * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument > * is the count of remaining callbacks, and "done" is the piggybacking count. > */ > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index f6880052b917..7680fc275036 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3312,11 +3312,16 @@ static void _rcu_barrier(struct rcu_state *rsp) > continue; > rdp = per_cpu_ptr(rsp->rda, cpu); > if (rcu_is_nocb_cpu(cpu)) { > - _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, > - rsp->n_barrier_done); > - atomic_inc(&rsp->barrier_cpu_count); > - __call_rcu(&rdp->barrier_head, rcu_barrier_callback, > - rsp, cpu, 0); > + if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) { > + _rcu_barrier_trace(rsp, "OfflineNoCB", cpu, > + rsp->n_barrier_done); > + } else { > + _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, > + rsp->n_barrier_done); > + atomic_inc(&rsp->barrier_cpu_count); > + __call_rcu(&rdp->barrier_head, > + rcu_barrier_callback, rsp, cpu, 0); > + } > } else if (ACCESS_ONCE(rdp->qlen)) { > _rcu_barrier_trace(rsp, "OnlineQ", cpu, > rsp->n_barrier_done); > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h > index 4beab3d2328c..8e7b1843896e 100644 > --- a/kernel/rcu/tree.h > +++ b/kernel/rcu/tree.h > @@ -587,6 +587,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, > int cpu); > static void print_cpu_stall_info_end(void); > static void zero_cpu_stall_ticks(struct rcu_data *rdp); > static void increment_cpu_stall_ticks(void); > +static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu); > static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq); > static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); > static void rcu_init_one_nocb(struct rcu_node *rnp); > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 927c17b081c7..68c5b23b7173 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -2050,6 +2050,33 @@ static void wake_nocb_leader(struct rcu_data *rdp, > bool force) > } > > /* > + * Does the specified CPU need an RCU callback for the specified flavor > + * of rcu_barrier()? > + */ > +static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) > +{ > + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); > + struct rcu_head *rhp; > + > + /* No-CBs CPUs might have callbacks on any of three lists. */ > + rhp = ACCESS_ONCE(rdp->nocb_head); > + if (!rhp) > + rhp = ACCESS_ONCE(rdp->nocb_gp_head); > + if (!rhp) > + rhp = ACCESS_ONCE(rdp->nocb_follower_head); > + > + /* Having no rcuo kthread but CBs after scheduler starts is bad! */ > + if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) { > + /* RCU callback enqueued before CPU first came online??? */ > + pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", > + cpu, rhp->func); > + WARN_ON_ONCE(1); > + } > + > + return !!rhp; > +} > + > +/* > * Enqueue the specified string of rcu_head structures onto the specified > * CPU's no-CBs lists. The CPU is specified by rdp, the head of the > * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy > @@ -2646,6 +2673,10 @@ static bool init_nocb_callback_list(struct rcu_data > *rdp) > > #else /* #ifdef CONFIG_RCU_NOCB_CPU */ > > +static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) > +{ > +} > + > static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) > { > } > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
