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locking/lockdep: Use sched_clock() for random numbers

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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
This commit is contained in:
Sebastian Andrzej Siewior 2022-05-17 11:16:14 +02:00 committed by Peter Zijlstra
parent b13baccc38
commit 4051a81774
1 changed files with 1 additions and 1 deletions
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2
kernel/locking/lockdep.c
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@ -5432,7 +5432,7 @@ static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)
* be guessable and still allows some pin nesting in * be guessable and still allows some pin nesting in
* our u32 pin_count. * our u32 pin_count.
*/ */
cookie.val = 1 + (prandom_u32() >> 16); cookie.val = 1 + (sched_clock() & 0xffff);
hlock->pin_count += cookie.val; hlock->pin_count += cookie.val;
return cookie; return cookie;
} }