rcutorture: Allow pointer leaks to test diagnostic code

This commit adds an rcutorture.leakpointer module parameter that
intentionally leaks an RCU-protected pointer out of the RCU read-side
critical section and checks to see if the corresponding grace period
has elapsed, emitting a WARN_ON_ONCE() if so.  This module parameter can
be used to test facilities like CONFIG_RCU_STRICT_GRACE_PERIOD that end
grace periods quickly.

While in the area, also document rcutorture.irqreader, which was
previously left out.

Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdc1f33..6d984f1 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4269,6 +4269,18 @@
                        are zero, rcutorture acts as if is interpreted
                        they are all non-zero.
 
+       rcutorture.irqreader= [KNL]
+                       Run RCU readers from irq handlers, or, more
+                       accurately, from a timer handler.  Not all RCU
+                       flavors take kindly to this sort of thing.
+
+       rcutorture.leakpointer= [KNL]
+                       Leak an RCU-protected pointer out of the reader.
+                       This can of course result in splats, and is
+                       intended to test the ability of things like
+                       CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
+                       such leaks.
+
        rcutorture.n_barrier_cbs= [KNL]
                        Set callbacks/threads for rcu_barrier() testing.
 

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 983f82f..916ea4f 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -87,6 +87,7 @@ torture_param(bool, gp_normal, false,
             "Use normal (non-expedited) GP wait primitives");
 torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives");
 torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
+torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers");
 torture_param(int, n_barrier_cbs, 0,
             "# of callbacks/kthreads for barrier testing");
 torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
@@ -1401,6 +1402,9 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
        preempt_enable();
        rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
        WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);
+       // This next splat is expected behavior if leakpointer, especially
+       // for CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels.
+       WARN_ON_ONCE(leakpointer && READ_ONCE(p->rtort_pipe_count) > 1);
 
        /* If error or close call, record the sequence of reader protections. */
        if ((pipe_count > 1 || completed > 1) && !xchg(&err_segs_recorded, 1)) {