locking/lockdep: Use sched_clock() for random numbers

Since the rewrote of prandom_u32(), in the commit mentioned below, the
function uses sleeping locks which extracing random numbers and filling
the batch.
This breaks lockdep on PREEMPT_RT because lock_pin_lock() disables
interrupts while calling __lock_pin_lock(). This can't be moved earlier
because the main user of the function (rq_pin_lock()) invokes that
function after disabling interrupts in order to acquire the lock.

The cookie does not require random numbers as its goal is to provide a
random value in order to notice unexpected "unlock + lock" sites.

Use sched_clock() to provide random numbers.

Fixes: a0103f4d86f88 ("random32: use real rng for non-deterministic randomness")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YoNn3pTkm5+QzE5k@linutronix.de

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 81e8728..f06b91c 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5432,7 +5432,7 @@ static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)
                         * be guessable and still allows some pin nesting in
                         * our u32 pin_count.
                         */
-                       cookie.val = 1 + (prandom_u32() >> 16);
+                       cookie.val = 1 + (sched_clock() & 0xffff);
                        hlock->pin_count += cookie.val;
                        return cookie;
                }