rcu: make rcutorture even more vicious: invoke RCU readers from irq handlers (timers)

This patch allows torturing RCU from irq handlers (timers, in this case).
A new module parameter irqreader enables such additional torturing,
and is enabled by default.  Variants of RCU that do not tolerate readers
being called from irq handlers (e.g., SRCU) ignore irqreader.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: josh@freedesktop.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: dino@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: torvalds@linux-foundation.org
Cc: vegard.nossum@gmail.com
Cc: adobriyan@gmail.com
Cc: oleg@tv-sign.ru
Cc: bunk@kernel.org
Cc: rjw@sisk.pl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 9 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 516527d4bc55..a342b6e1cc10 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -30,10 +30,10 @@ MODULE PARAMETERS
 
 This module has the following parameters:
 
-nreaders        This is the number of RCU reading threads supported.
-                The default is twice the number of CPUs.  Why twice?
-                To properly exercise RCU implementations with preemptible
-                read-side critical sections.
+irqreaders      Says to invoke RCU readers from irq level.  This is currently
+                done via timers.  Defaults to "1" for variants of RCU that
+                permit this.  (Or, more accurately, variants of RCU that do
+                -not- permit this know to ignore this variable.)
 
 nfakewriters    This is the number of RCU fake writer threads to run.  Fake
                 writer threads repeatedly use the synchronous "wait for
@@ -44,6 +44,16 @@ nfakewriters	This is the number of RCU fake writer threads to run.  Fake
                 to trigger special cases caused by multiple writers, such as
                 the synchronize_srcu() early return optimization.
 
+nreaders        This is the number of RCU reading threads supported.
+                The default is twice the number of CPUs.  Why twice?
+                To properly exercise RCU implementations with preemptible
+                read-side critical sections.
+
+shuffle_interval
+                The number of seconds to keep the test threads affinitied
+                to a particular subset of the CPUs, defaults to 3 seconds.
+                Used in conjunction with test_no_idle_hz.
+
 stat_interval   The number of seconds between output of torture
                 statistics (via printk()).  Regardless of the interval,
                 statistics are printed when the module is unloaded.
@@ -51,11 +61,6 @@ stat_interval	The number of seconds between output of torture
                 be printed -only- when the module is unloaded, and this
                 is the default.
 
-shuffle_interval
-                The number of seconds to keep the test threads affinitied
-                to a particular subset of the CPUs, defaults to 3 seconds.
-                Used in conjunction with test_no_idle_hz.
-
 stutter         The length of time to run the test before pausing for this
                 same period of time.  Defaults to "stutter=5", so as
                 to run and pause for (roughly) five-second intervals.