linux-kernel - Re: two RCU torture bugs

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Date:	Mon, 24 Aug 2015 11:50:36 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	josh@...htriplett.org, linux-kernel@...r.kernel.org
Subject: Re: two RCU torture bugs

On Sun, Aug 23, 2015 at 10:29:15PM -0700, Paul E. McKenney wrote:
> On Sun, Aug 23, 2015 at 10:07:49PM -0700, David Miller wrote:
> > 
> > 1) Doc bug, documentation mentions torture_type such as "rcu_sync",
> >    but those don't seem to exist.
> > 
> > 2) If you specify an unrecognized type, the module cannot be unloaded.
> >    Amusingly it says that it cannot unload because the unrecognized
> >    torture test type you requested is "running" :-)
> 
> Clearly Iftekhar was mutating the wrong code.  ;-)
> 
> And clearly I need to occasionally test failure cases.  There is code that
> is supposed to unwind upon failure, but it has apparently bitrotted...

Do the following pair of untested patches help?

							Thanx, Paul

------------------------------------------------------------------------

commit d568705d102ceb61884a3a8b77a98168094acbca
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Mon Aug 24 11:37:58 2015 -0700

    rcutorture: Fix module unwind when bad torture_type specified
    
    The rcutorture module has a list of torture types, and specifying a
    type not on this list is supposed to cleanly fail the module load.
    Unfortunately, the "fail" happens without the "cleanly".  This commit
    therefore adds the needed clean-up after an incorrect torture_type.
    
    Reported-by: David Miller <davem@...emloft.net>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f9ec6cbe77d3..9c4f5cd86532 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -695,7 +695,7 @@ static bool __maybe_unused torturing_tasks(void)
 
 #define RCUTORTURE_TASKS_OPS
 
-static bool torturing_tasks(void)
+static bool __maybe_unused torturing_tasks(void)
 {
 	return false;
 }
@@ -1742,8 +1742,8 @@ rcu_torture_init(void)
 		for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
 			pr_alert(" %s", torture_ops[i]->name);
 		pr_alert("\n");
-		torture_init_end();
-		return -EINVAL;
+		firsterr = -EINVAL;
+		goto unwind;
 	}
 	if (cur_ops->fqs == NULL && fqs_duration != 0) {
 		pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");

------------------------------------------------------------------------

commit 20f34145cfbba04b44b8fbd29689bdcc0ab0b303
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Mon Aug 24 11:46:00 2015 -0700

    documentation: Catch up list of torture_type options
    
    This commit rids the documentation of long-obsolete torture_type options
    such as rcu_sync and adds new ones such as tasks.  Also add verbiage
    noting the fact that rcutorture now concurrently tests the asynchrounous,
    synchronous, expedited synchronous, and polling grace-period primitives.
    
    Reported-by: David Miller <davem@...emloft.net>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index dac02a6219b1..118e7c176ce7 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -166,40 +166,27 @@ test_no_idle_hz	Whether or not to test the ability of RCU to operate in
 
 torture_type	The type of RCU to test, with string values as follows:
 
-		"rcu":  rcu_read_lock(), rcu_read_unlock() and call_rcu().
-
-		"rcu_sync":  rcu_read_lock(), rcu_read_unlock(), and
-			synchronize_rcu().
-
-		"rcu_expedited": rcu_read_lock(), rcu_read_unlock(), and
-			synchronize_rcu_expedited().
+		"rcu":  rcu_read_lock(), rcu_read_unlock() and call_rcu(),
+			along with expedited, synchronous, and polling
+			variants.
 
 		"rcu_bh": rcu_read_lock_bh(), rcu_read_unlock_bh(), and
-			call_rcu_bh().
-
-		"rcu_bh_sync": rcu_read_lock_bh(), rcu_read_unlock_bh(),
-			and synchronize_rcu_bh().
+			call_rcu_bh(), along with expedited and synchronous
+			variants.
 
-		"rcu_bh_expedited": rcu_read_lock_bh(), rcu_read_unlock_bh(),
-			and synchronize_rcu_bh_expedited().
+		"rcu_busted": This tests an intentionally incorrect version
+			of RCU in order to help test rcutorture itself.
 
 		"srcu": srcu_read_lock(), srcu_read_unlock() and
-			call_srcu().
-
-		"srcu_sync": srcu_read_lock(), srcu_read_unlock() and
-			synchronize_srcu().
-
-		"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
-			synchronize_srcu_expedited().
+			call_srcu(), along with expedited and
+			synchronous variants.
 
 		"sched": preempt_disable(), preempt_enable(), and
-			call_rcu_sched().
-
-		"sched_sync": preempt_disable(), preempt_enable(), and
-			synchronize_sched().
+			call_rcu_sched(), along with expedited,
+			synchronous, and polling variants.
 
-		"sched_expedited": preempt_disable(), preempt_enable(), and
-			synchronize_sched_expedited().
+		"tasks": voluntary context switch and call_rcu_tasks(),
+			along with expedited and synchronous variants.
 
 		Defaults to "rcu".
 

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