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SubjectRe: [rcutorture] 82e310033d: WARNING:possible_recursive_locking_detected
hi Paul,

On Tue, Dec 28, 2021 at 04:06:09PM -0800, Paul E. McKenney wrote:
> 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?

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

=========================================================================================
compiler/kconfig/rootfs/runtime/tbox_group/test/testcase/torture_type:
gcc-9/i386-randconfig-a002-20211003/debian-i386-20191205.cgz/300s/vm-snb-i386/default/rcutorture/rcu

commit:
next-20211224
917801238dcca ("rcutorture: Fix rcu_fwd_mutex deadlock")

next-20211224 917801238dccaf61a63ffe77890
---------------- ---------------------------
fail:runs %reproduction fail:runs
| | |
3:100 -1% 2:100 dmesg.BUG:sleeping_function_called_from_invalid_context_at_kernel/locking/mutex.c
2:100 -2% :100 dmesg.BUG:workqueue_lockup-pool
1:100 -1% :100 dmesg.EIP:clear_user
2:100 2% 4:100 dmesg.EIP:rcu_torture_fwd_prog_cr
15:100 -3% 12:100 dmesg.EIP:rcutorture_oom_notify
2:100 -2% :100 dmesg.Kernel_panic-not_syncing:System_is_deadlocked_on_memory
9:100 -5% 4:100 dmesg.Mem-Info
2:100 -2% :100 dmesg.Out_of_memory_and_no_killable_processes
2:100 2% 4:100 dmesg.WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_fwd_prog_cr[rcutorture]
15:100 -3% 12:100 dmesg.WARNING:at_kernel/rcu/rcutorture.c:#rcutorture_oom_notify[rcutorture]
15:100 -15% :100 dmesg.WARNING:possible_recursive_locking_detected <--------
3:100 -1% 2:100 dmesg.invoked_oom-killer:gfp_mask=0x
6:100 -4% 2:100 dmesg.page_allocation_failure:order:#,mode:#(GFP_NOWAIT|__GFP_COMP),nodemask=(null)
100:100 0% 100:100 dmesg.sysctl_table_check_failed


>
> 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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