[PATCH 11/23] locktorture: Add acq_writer_lim to complain about long acquistion times

Frederic Weisbecker
2023-10-10T12:00:47Z

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>
---
kernel/locking/locktorture.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index c8c322e69a90..296815ef67ae 100644
--- 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)
{
- struct lock_stress_stats *lwsp = arg;
- int tid = lwsp - cxt.lwsa;
- DEFINE_TORTURE_RANDOM(rand);
+ unsigned long j;
+ unsigned long j1;
u32 lockset_mask;
+ struct lock_stress_stats *lwsp = arg;
+ DEFINE_TORTURE_RANDOM(rand);
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);
--
2.34.1