[PATCH tip/core/rcu 13/14] rcutorture: Allow pointer leaks to test diagnostic code

paulmck
2020-08-31T18:04:40Z

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>
---
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)) {
--
2.9.5