rcu: Add CPU-stall capability to rcutorture

Add module parameters to rcutorture that induce a CPU stall.
The stall_cpu parameter specifies how long to stall in seconds,
defaulting to zero, which indicates no stalling is to be undertaken.
The stall_cpu_holdoff parameter specifies how many seconds after
insmod (or boot, if rcutorture is built into the kernel) that this
stall is to start.  The default value for stall_cpu_holdoff is ten
seconds.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index d25be872ae33..375d3fb71437 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -86,6 +86,24 @@ shutdown_secs	The number of seconds to run the test before terminating
                 zero, which disables test termination and system shutdown.
                 This capability is useful for automated testing.
 
+stall_cpu       The number of seconds that a CPU should be stalled while
+                within both an rcu_read_lock() and a preempt_disable().
+                This stall happens only once per rcutorture run.
+                If you need multiple stalls, use modprobe and rmmod to
+                repeatedly run rcutorture.  The default for stall_cpu
+                is zero, which prevents rcutorture from stalling a CPU.
+
+                Note that attempts to rmmod rcutorture while the stall
+                is ongoing will hang, so be careful what value you
+                choose for this module parameter!  In addition, too-large
+                values for stall_cpu might well induce failures and
+                warnings in other parts of the kernel.  You have been
+                warned!
+
+stall_cpu_holdoff
+                The number of seconds to wait after rcutorture starts
+                before stalling a CPU.  Defaults to 10 seconds.
+
 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.