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SubjectRe: [rcutorture] 82e310033d: WARNING:possible_recursive_locking_detected
On Tue, Dec 28, 2021 at 11:11:35PM +0800, kernel test robot wrote:
>
>
> Greeting,
>
> FYI, we noticed the following commit (built with gcc-9):
>
> commit: 82e310033d7c21a7a88427f14e0dad78d731a5cd ("rcutorture: Enable multiple concurrent callback-flood kthreads")
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>
> in testcase: rcutorture
> version:
> with following parameters:
>
> runtime: 300s
> test: default
> torture_type: rcu
>
> test-description: rcutorture is rcutorture kernel module load/unload test.
> test-url: https://www.kernel.org/doc/Documentation/RCU/torture.txt
>
>
> on test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -m 4G
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
> +-------------------------------------------------------------------------------+------------+------------+
> | | 12e885433d | 82e310033d |
> +-------------------------------------------------------------------------------+------------+------------+
> | boot_successes | 95 | 47 |
> | boot_failures | 31 | 25 |
> | invoked_oom-killer:gfp_mask=0x | 5 | 4 |
> | Mem-Info | 10 | 16 |
> | WARNING:at_kernel/rcu/rcutorture.c:#rcutorture_oom_notify[rcutorture] | 24 | 15 |
> | EIP:rcutorture_oom_notify | 24 | 15 |
> | page_allocation_failure:order:#,mode:#(GFP_NOWAIT|__GFP_COMP),nodemask=(null) | 5 | 12 |
> | WARNING:possible_recursive_locking_detected | 0 | 15 |
> | WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_fwd_prog.cold[rcutorture] | 0 | 6 |
> | EIP:rcu_torture_fwd_prog.cold | 0 | 6 |
> +-------------------------------------------------------------------------------+------------+------------+
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@intel.com>

Good catch! Does this following patch address it?

Thanx, Paul

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

commit dd47cbdcc2f72ba3df1248fb7fe210acca18d09c
Author: Paul E. McKenney <paulmck@kernel.org>
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 <oliver.sang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

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);
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