Commit d6855142 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 299c7d94

Documentation/admin-guide/kernel-parameters.txt

+12 −0
Original line number Diff line number Diff line
@@ -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.

kernel/rcu/rcutorture.c

+4 −0
Original line number Diff line number Diff line
@@ -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)) {

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