Re: next: Commit 'mm: Prevent __alloc_pages_nodemask() RCU CPU stall ...' causing hang on sparc32 qemu

[Guenter Roeck]

On 11/29/2016 11:02 PM, Paul E. McKenney wrote:
> On Tue, Nov 29, 2016 at 08:32:51PM -0800, Guenter Roeck wrote:
> > On 11/29/2016 05:28 PM, Paul E. McKenney wrote:
> > > On Tue, Nov 29, 2016 at 01:23:08PM -0800, Guenter Roeck wrote:
> > > > Hi Paul,
> > > >
> > > > most of my qemu tests for sparc32 targets started to fail in next-20161129.
> > > > The problem is only seen in SMP builds; non-SMP builds are fine.
> > > > Bisect points to commit 2d66cccd73436 ("mm: Prevent __alloc_pages_nodemask()
> > > > RCU CPU stall warnings"); reverting that commit fixes the problem.
> > > >
> > > > Test scripts are available at:
> > > > 	https://github.com/groeck/linux-build-test/tree/master/rootfs/sparc
> > > > Test results are at:
> > > > 	https://github.com/groeck/linux-build-test/tree/master/rootfs/sparc
> > > >
> > > > Bisect log is attached.
> > > >
> > > > Please let me know if there is anything I can do to help tracking down the
> > > > problem.
> > >
> > > Apologies!!!  Does the patch below help?
> > No, sorry, it doesn't make a difference.
>
> Interesting...  Could you please send me the build failure messages?

There is no failure message; it just hangs until I abort the qemu session.

http://kerneltests.org/builders/qemu-sparc-next/builds/532/steps/qemubuildcommand/logs/stdio

Guenter

> 							Thanx, Paul
>
> > Guenter
> >
> > > 							Thanx, Paul
> > >
> > > ------------------------------------------------------------------------
> > >
> > > commit 97708e737e2a55fed4bdbc005bf05ea909df6b73
> > > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > > Date:   Tue Nov 29 11:06:05 2016 -0800
> > >
> > >    rcu: Allow boot-time use of cond_resched_rcu_qs()
> > >
> > >    The cond_resched_rcu_qs() macro is used to force RCU quiescent states into
> > >    long-running in-kernel loops.  However, some of these loops can execute
> > >    during early boot when interrupts are disabled, and during which time
> > >    it is therefore illegal to enter the scheduler.  This commit therefore
> > >    makes cond_resched_rcu_qs() be a no-op during early boot.
> > >
> > >    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > >
> > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > index 525ca34603b7..b6944cc19a07 100644
> > > --- a/include/linux/rcupdate.h
> > > +++ b/include/linux/rcupdate.h
> > > @@ -423,7 +423,7 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
> > >  */
> > > #define cond_resched_rcu_qs() \
> > > do { \
> > > -	if (!cond_resched()) \
> > > +	if (!is_idle_task(current) && !cond_resched()) \
> > > 		rcu_note_voluntary_context_switch(current); \
> > > } while (0)
> > >
> > > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> > > index 7232d199a81c..20f5990deeee 100644
> > > --- a/include/linux/rcutiny.h
> > > +++ b/include/linux/rcutiny.h
> > > @@ -228,6 +228,7 @@ static inline void exit_rcu(void)
> > > extern int rcu_scheduler_active __read_mostly;
> > > void rcu_scheduler_starting(void);
> > > #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
> > > +#define rcu_scheduler_active false
> > > static inline void rcu_scheduler_starting(void)
> > > {
> > > }