Re: [PATCH tip/core/rcu 35/55] rcutorture: Fix rcutorture shutdown races

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Mon, Feb 17, 2014 at 04:32:59PM -0800, Josh Triplett wrote:
> On Mon, Feb 17, 2014 at 02:12:39PM -0800, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > 
> > Not all of the rcutorture kthreads waited for kthread_should_stop()
> > before returning from their top-level functions, and none of them
> > used torture_shutdown_absorb() properly.  These problems can result in
> > segfaults and hangs at shutdown time, and some recent changes perturbed
> > timing sufficiently to make them much more probable.  This commit
> > therefore creates a torture_kthread_stopping() function that does the
> > proper kthread shutdown dance in one centralized location.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> One comment below.
> 
> >  include/linux/torture.h |  3 ++-
> >  kernel/rcu/rcutorture.c | 39 +++++++++++----------------------------
> >  kernel/torture.c        | 26 ++++++++++++++++++++++----
> >  3 files changed, 35 insertions(+), 33 deletions(-)
> > 
> > diff --git a/include/linux/torture.h b/include/linux/torture.h
> > index 513b85f98585..db9bc7756a32 100644
> > --- a/include/linux/torture.h
> > +++ b/include/linux/torture.h
> > @@ -45,7 +45,7 @@
> >  #define TOROUT_STRING(s) \
> >  	pr_alert("%s" TORTURE_FLAG s "\n", torture_type)
> >  #define VERBOSE_TOROUT_STRING(s) \
> > -	do { if (verbose) pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0)
> > +	do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)
> 
> This change is completely unrelated to the change described in the
> commit message.  This should not be part of this commit.

Turns out that I left out a hunk applying this in torture_kthread_stopping().
I have added that hunk and updated the commit log explaining why the change
to VERBOSE_TOROUT_STRING() is required.

								Thanx, Paul

> >  #define VERBOSE_TOROUT_ERRSTRING(s) \
> >  	do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0)
> >  
> > @@ -88,5 +88,6 @@ void torture_init_end(void);
> >  bool torture_cleanup(void);
> >  bool torture_must_stop(void);
> >  bool torture_must_stop_irq(void);
> > +void torture_kthread_stopping(char *title);
> >  
> >  #endif /* __LINUX_TORTURE_H */
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index aaca2350e0e4..6d12fd18d97f 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -601,12 +601,13 @@ checkwait:	stutter_wait("rcu_torture_boost");
> >  	} while (!torture_must_stop());
> >  
> >  	/* Clean up and exit. */
> > -	VERBOSE_TOROUT_STRING("rcu_torture_boost task stopping");
> > -	torture_shutdown_absorb("rcu_torture_boost");
> > -	while (!kthread_should_stop() || rbi.inflight)
> > +	while (!kthread_should_stop() || rbi.inflight) {
> > +		torture_shutdown_absorb("rcu_torture_boost");
> >  		schedule_timeout_uninterruptible(1);
> > +	}
> >  	smp_mb(); /* order accesses to ->inflight before stack-frame death. */
> >  	destroy_rcu_head_on_stack(&rbi.rcu);
> > +	torture_kthread_stopping("rcu_torture_boost");
> >  	return 0;
> >  }
> >  
> > @@ -637,10 +638,7 @@ rcu_torture_fqs(void *arg)
> >  		}
> >  		stutter_wait("rcu_torture_fqs");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_fqs task stopping");
> > -	torture_shutdown_absorb("rcu_torture_fqs");
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_uninterruptible(1);
> > +	torture_kthread_stopping("rcu_torture_fqs");
> >  	return 0;
> >  }
> >  
> > @@ -709,10 +707,7 @@ rcu_torture_writer(void *arg)
> >  		rcutorture_record_progress(++rcu_torture_current_version);
> >  		stutter_wait("rcu_torture_writer");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_writer task stopping");
> > -	torture_shutdown_absorb("rcu_torture_writer");
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_uninterruptible(1);
> > +	torture_kthread_stopping("rcu_torture_writer");
> >  	return 0;
> >  }
> >  
> > @@ -747,10 +742,7 @@ rcu_torture_fakewriter(void *arg)
> >  		stutter_wait("rcu_torture_fakewriter");
> >  	} while (!torture_must_stop());
> >  
> > -	VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task stopping");
> > -	torture_shutdown_absorb("rcu_torture_fakewriter");
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_uninterruptible(1);
> > +	torture_kthread_stopping("rcu_torture_fakewriter");
> >  	return 0;
> >  }
> >  
> > @@ -891,12 +883,9 @@ rcu_torture_reader(void *arg)
> >  		schedule();
> >  		stutter_wait("rcu_torture_reader");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_reader task stopping");
> > -	torture_shutdown_absorb("rcu_torture_reader");
> >  	if (irqreader && cur_ops->irq_capable)
> >  		del_timer_sync(&t);
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_uninterruptible(1);
> > +	torture_kthread_stopping("rcu_torture_reader");
> >  	return 0;
> >  }
> >  
> > @@ -1009,7 +998,7 @@ rcu_torture_stats(void *arg)
> >  		rcu_torture_stats_print();
> >  		torture_shutdown_absorb("rcu_torture_stats");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_stats task stopping");
> > +	torture_kthread_stopping("rcu_torture_stats");
> >  	return 0;
> >  }
> >  
> > @@ -1170,12 +1159,9 @@ static int rcu_torture_barrier_cbs(void *arg)
> >  		if (atomic_dec_and_test(&barrier_cbs_count))
> >  			wake_up(&barrier_wq);
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_barrier_cbs task stopping");
> > -	torture_shutdown_absorb("rcu_torture_barrier_cbs");
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_interruptible(1);
> >  	cur_ops->cb_barrier();
> >  	destroy_rcu_head_on_stack(&rcu);
> > +	torture_kthread_stopping("rcu_torture_barrier_cbs");
> >  	return 0;
> >  }
> >  
> > @@ -1206,10 +1192,7 @@ static int rcu_torture_barrier(void *arg)
> >  		n_barrier_successes++;
> >  		schedule_timeout_interruptible(HZ / 10);
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("rcu_torture_barrier task stopping");
> > -	torture_shutdown_absorb("rcu_torture_barrier");
> > -	while (!kthread_should_stop())
> > -		schedule_timeout_interruptible(1);
> > +	torture_kthread_stopping("rcu_torture_barrier");
> >  	return 0;
> >  }
> >  
> > diff --git a/kernel/torture.c b/kernel/torture.c
> > index 12a5807fb4e9..6f1c6600d183 100644
> > --- a/kernel/torture.c
> > +++ b/kernel/torture.c
> > @@ -169,7 +169,7 @@ torture_onoff(void *arg)
> >  		}
> >  		schedule_timeout_interruptible(onoff_interval);
> >  	}
> > -	VERBOSE_TOROUT_STRING("torture_onoff task stopping");
> > +	torture_kthread_stopping("torture_onoff");
> >  	return 0;
> >  }
> >  
> > @@ -370,7 +370,7 @@ static int torture_shuffle(void *arg)
> >  		torture_shuffle_tasks();
> >  		torture_shutdown_absorb("torture_shuffle");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("torture_shuffle task stopping");
> > +	torture_kthread_stopping("torture_shuffle");
> >  	return 0;
> >  }
> >  
> > @@ -465,7 +465,7 @@ static int torture_shutdown(void *arg)
> >  		jiffies_snap = jiffies;
> >  	}
> >  	if (torture_must_stop()) {
> > -		VERBOSE_TOROUT_STRING("torture_shutdown task stopping");
> > +		torture_kthread_stopping("torture_shutdown");
> >  		return 0;
> >  	}
> >  
> > @@ -583,7 +583,7 @@ static int torture_stutter(void *arg)
> >  		ACCESS_ONCE(stutter_pause_test) = 0;
> >  		torture_shutdown_absorb("torture_stutter");
> >  	} while (!torture_must_stop());
> > -	VERBOSE_TOROUT_STRING("torture_stutter task stopping");
> > +	torture_kthread_stopping("torture_stutter");
> >  	return 0;
> >  }
> >  
> > @@ -696,3 +696,21 @@ bool torture_must_stop_irq(void)
> >  	return ACCESS_ONCE(fullstop) != FULLSTOP_DONTSTOP;
> >  }
> >  EXPORT_SYMBOL_GPL(torture_must_stop_irq);
> > +
> > +/*
> > + * Each kthread must wait for kthread_should_stop() before returning from
> > + * its top-level function, otherwise segfaults ensue.  This function
> > + * prints a "stopping" message and waits for kthread_should_stop(), and
> > + * should be called from all torture kthreads immediately prior to
> > + * returning.
> > + */
> > +void torture_kthread_stopping(char *title)
> > +{
> > +	if (verbose)
> > +		pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, title);
> > +	while (!kthread_should_stop()) {
> > +		torture_shutdown_absorb(title);
> > +		schedule_timeout_uninterruptible(1);
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(torture_kthread_stopping);
> > -- 
> > 1.8.1.5
> > 
>