[tip: locking/urgent] locking/lockdep: Use sched_clock() for random numbers
From: tip-bot2 for Sebastian Andrzej Siewior
Date: Mon Jun 13 2022 - 04:36:27 EST
The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: 4051a81774d6d8e28192742c26999d6f29bc0e68
Gitweb: https://git.kernel.org/tip/4051a81774d6d8e28192742c26999d6f29bc0e68
Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
AuthorDate: Tue, 17 May 2022 11:16:14 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 13 Jun 2022 10:29:57 +02:00
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@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/YoNn3pTkm5+QzE5k@xxxxxxxxxxxxx
---
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 81e8728..f06b91c 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;
}