linux-kernel - [RFC PATCH] lib/test_lockup: Minimum fix to get it compiled on PREEMPT

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Date:   Wed, 28 Oct 2020 19:10:41 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC PATCH] lib/test_lockup: Minimum fix to get it compiled on
 PREEMPT_RT

On PREEMPT_RT the locks are quite different so they can't be tested as
it is done below. The alternative is to test for the waitlock within
rtmutex.

This is the bare minim to get it compiled. Problems which exist on
PREEMP_RT:
- none of the locks (spinlock_t, rwlock_t, mutex_t, rw_semaphore) may be
  acquired with disabled preemption or interrupts.
  If I read the code correct the it is possible to acquire a mutex_t with
  disabled interrupts.
  I don't know how to obtain a lock pointer. Technically they are not
  exported to userland.

- memory can not be allocated with disabled preemption or interrupts
  even with GFP_ATOMIC.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 lib/test_lockup.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index f1a020bcc763e..864554e769738 100644
--- a/lib/test_lockup.c
+++ b/lib/test_lockup.c
@@ -480,6 +480,21 @@ static int __init test_lockup_init(void)
 		return -EINVAL;
 
 #ifdef CONFIG_DEBUG_SPINLOCK
+#ifdef CONFIG_PREEMPT_RT
+	if (test_magic(lock_spinlock_ptr,
+		       offsetof(spinlock_t, lock.wait_lock.magic),
+		       SPINLOCK_MAGIC) ||
+	    test_magic(lock_rwlock_ptr,
+		       offsetof(rwlock_t, rtmutex.wait_lock.magic),
+		       SPINLOCK_MAGIC) ||
+	    test_magic(lock_mutex_ptr,
+		       offsetof(struct mutex, lock.wait_lock.magic),
+		       SPINLOCK_MAGIC) ||
+	    test_magic(lock_rwsem_ptr,
+		       offsetof(struct rw_semaphore, rtmutex.wait_lock.magic),
+		       SPINLOCK_MAGIC))
+		return -EINVAL;
+#else
 	if (test_magic(lock_spinlock_ptr,
 		       offsetof(spinlock_t, rlock.magic),
 		       SPINLOCK_MAGIC) ||
@@ -493,6 +508,7 @@ static int __init test_lockup_init(void)
 		       offsetof(struct rw_semaphore, wait_lock.magic),
 		       SPINLOCK_MAGIC))
 		return -EINVAL;
+#endif
 #endif
 
 	if ((wait_state != TASK_RUNNING ||
-- 
2.28.0