[tip: core/rcu] rcutorture: Allow pointer leaks to test diagnostic code

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     d685514260e21aabd65a9aa8be045766bdaa0549
Gitweb:        https://git.kernel.org/tip/d685514260e21aabd65a9aa8be045766bdaa0549
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Tue, 11 Aug 2020 10:33:39 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 24 Aug 2020 18:45:36 -07:00

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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++
 kernel/rcu/rcutorture.c                         |  4 ++++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdc1f33..6d984f1 100644
--- 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
--- 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)) {