lib/test_lockup.c: 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 minimun 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.

Link: https://lkml.kernel.org/r/20201028181041.xyeothhkouc3p4md@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index f1a020b..864554e 100644 (file)
--- 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) ||
@@ -494,6 +509,7 @@ static int __init test_lockup_init(void)
                       SPINLOCK_MAGIC))
                return -EINVAL;
 #endif
+#endif
 
        if ((wait_state != TASK_RUNNING ||
             (call_cond_resched && !reacquire_locks) ||