linux-kernel - Re: [PATCH] kfence: Avoid stalling work queue task without allocations

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Date:   Fri, 13 Nov 2020 09:57:54 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>, rcu@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] kfence: Avoid stalling work queue task without
 allocations

On Thu, Nov 12, 2020 at 09:54:06AM -0800, Paul E. McKenney wrote:
> On Thu, Nov 12, 2020 at 05:14:39PM +0100, Marco Elver wrote:

[ . . . ]

> > | [  334.160218] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 15s!
> 
> It might be instructive to cause this code to provoke a backtrace.
> I suggest adding something like "trigger_single_cpu_backtrace(cpu)"
> in kernel/workqueue.c's function named wq_watchdog_timer_fn()
> somewhere within its "if" statement that is preceded with the "did we
> stall?" comment.  Or just search for "BUG: workqueue lockup - pool"
> within kernel/workqueue.c.

And I did get a small but unexpected gift of time, so here is an
(untested) patch.

							Thanx, Paul

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

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 437935e..f3d4ff7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5792,6 +5792,7 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
 			pr_cont_pool_info(pool);
 			pr_cont(" stuck for %us!\n",
 				jiffies_to_msecs(jiffies - pool_ts) / 1000);
+			trigger_single_cpu_backtrace(cpu);
 		}
 	}