locktorture: Add acq_writer_lim to complain about long acquistion times

This commit adds a locktorture.acq_writer_lim module parameter that
specifies the maximum number of jiffies that is expected to be consumed
by write-side lock acquisition.  If this limit is exceeded, a WARN_ONCE()
causes a splat.  Note that this limit applies to the main lock acquisition
only, not to any nested acquisitions.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index c8c322e69a90bc1dfe9ea50fe6da19edb0967b75..296815ef67aee47a96db096f62118739be03fe34 100644 (file)
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -33,6 +33,7 @@
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com>");
 
+torture_param(int, acq_writer_lim, 0, "Write_acquisition time limit (jiffies).");
 torture_param(int, long_hold, 100, "Do occasional long hold of lock (ms), 0=disable");
 torture_param(int, nested_locks, 0, "Number of nested locks (max = 8)");
 torture_param(int, nreaders_stress, -1, "Number of read-locking stress-test threads");
@@ -852,11 +853,13 @@ static struct lock_torture_ops percpu_rwsem_lock_ops = {
  */
 static int lock_torture_writer(void *arg)
 {
+       unsigned long j;
+       unsigned long j1;
+       u32 lockset_mask;
        struct lock_stress_stats *lwsp = arg;
-       int tid = lwsp - cxt.lwsa;
        DEFINE_TORTURE_RANDOM(rand);
-       u32 lockset_mask;
        bool skip_main_lock;
+       int tid = lwsp - cxt.lwsa;
 
        VERBOSE_TOROUT_STRING("lock_torture_writer task started");
        if (!rt_task(current))
@@ -883,12 +886,20 @@ static int lock_torture_writer(void *arg)
                        cxt.cur_ops->nested_lock(tid, lockset_mask);
 
                if (!skip_main_lock) {
+                       if (acq_writer_lim > 0)
+                               j = jiffies;
                        cxt.cur_ops->writelock(tid);
                        if (WARN_ON_ONCE(lock_is_write_held))
                                lwsp->n_lock_fail++;
                        lock_is_write_held = true;
                        if (WARN_ON_ONCE(atomic_read(&lock_is_read_held)))
                                lwsp->n_lock_fail++; /* rare, but... */
+                       if (acq_writer_lim > 0) {
+                               j1 = jiffies;
+                               WARN_ONCE(time_after(j1, j + acq_writer_lim),
+                                         "%s: Lock acquisition took %lu jiffies.\n",
+                                         __func__, j1 - j);
+                       }
                        lwsp->n_lock_acquired++;
 
                        cxt.cur_ops->write_delay(&rand);