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    Subject[PATCH 08/18] rcu: Eliminate rcu_gp_slow_unregister() false positive
    Date
    From: "Paul E. McKenney" <paulmck@kernel.org>

    When using rcutorture as a module, there are a number of conditions that
    can abort the modprobe operation, for example, when attempting to run
    both RCU CPU stall warning tests and forward-progress tests. This can
    cause rcu_torture_cleanup() to be invoked on the unwind path out of
    rcu_rcu_torture_init(), which will mean that rcu_gp_slow_unregister()
    is invoked without a matching rcu_gp_slow_register(). This will cause
    a splat because rcu_gp_slow_unregister() is passed rcu_fwd_cb_nodelay,
    which does not match a NULL pointer.

    This commit therefore forgives a mismatch involving a NULL pointer, thus
    avoiding this false-positive splat.

    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
    ---
    kernel/rcu/tree.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index aae515071ffd..a83ecab77917 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -1260,7 +1260,7 @@ EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
    /* Unregister a counter, with NULL for not caring which. */
    void rcu_gp_slow_unregister(atomic_t *rgssp)
    {
    - WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
    + WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL);

    WRITE_ONCE(rcu_gp_slow_suppress, NULL);
    }
    --
    2.34.1
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