hi Paul,

On Wed, Dec 29, 2021 at 09:24:41AM -0800, Paul E. McKenney wrote:

On Wed, Dec 29, 2021 at 10:01:21PM +0800, Oliver Sang wrote:

quoted

hi Paul,

we applied below patch upon next-20211224,
confirmed no "WARNING:possible_recursive_locking_detected" after patch.

Good to hear!  May I add your Tested-by?

sure (:

Tested-by: Oliver Sang <redacted>

Many of the remainder appear to be due to memory exhaustion, FWIW.

thanks for information

							Thanx, Paul

quoted

quoted

------------------------------------------------------------------------

commit dd47cbdcc2f72ba3df1248fb7fe210acca18d09c
Author: Paul E. McKenney [off-list ref]
Date:   Tue Dec 28 15:59:38 2021 -0800

    rcutorture: Fix rcu_fwd_mutex deadlock
    
    The rcu_torture_fwd_cb_hist() function acquires rcu_fwd_mutex, but is
    invoked from rcutorture_oom_notify() function, which hold this same
    mutex across this call.  This commit fixes the resulting deadlock.
    
    Reported-by: kernel test robot [off-list ref]
    Signed-off-by: Paul E. McKenney [off-list ref]

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 918a2ea34ba13..9190dce686208 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c

@@ -2184,7 +2184,6 @@ static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
 	for (i = ARRAY_SIZE(rfp->n_launders_hist) - 1; i > 0; i--)
 		if (rfp->n_launders_hist[i].n_launders > 0)
 			break;
-	mutex_lock(&rcu_fwd_mutex); // Serialize histograms.
 	pr_alert("%s: Callback-invocation histogram %d (duration %lu jiffies):",
 		 __func__, rfp->rcu_fwd_id, jiffies - rfp->rcu_fwd_startat);
 	gps_old = rfp->rcu_launder_gp_seq_start;

@@ -2197,7 +2196,6 @@ static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
 		gps_old = gps;
 	}
 	pr_cont("\n");
-	mutex_unlock(&rcu_fwd_mutex);
 }
 
 /* Callback function for continuous-flood RCU callbacks. */

@@ -2435,7 +2433,9 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
 			 n_launders, n_launders_sa,
 			 n_max_gps, n_max_cbs, cver, gps);
 		atomic_long_add(n_max_cbs, &rcu_fwd_max_cbs);
+		mutex_lock(&rcu_fwd_mutex); // Serialize histograms.
 		rcu_torture_fwd_cb_hist(rfp);
+		mutex_unlock(&rcu_fwd_mutex);
 	}
 	schedule_timeout_uninterruptible(HZ); /* Let CBs drain. */
 	tick_dep_clear_task(current, TICK_DEP_BIT_RCU);