From 4051a81774d6d8e28192742c26999d6f29bc0e68 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 17 May 2022 11:16:14 +0200 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/YoNn3pTkm5+QzE5k@linutronix.de --- kernel/locking/lockdep.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 81e87280513e..f06b91ca6482 100644 --- 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; }