Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 13 Nov 2020 09:57:54 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Marco Elver <elver@google.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Anders Roxell <anders.roxell@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jann Horn <jannh@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        kasan-dev <kasan-dev@googlegroups.com>, rcu@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] kfence: Avoid stalling work queue task without
 allocations
Message-ID: <20201113175754.GA6273@paulmck-ThinkPad-P72>
Reply-To: paulmck@kernel.org
References: <20201111133813.GA81547@elver.google.com>
 <20201111130543.27d29462@gandalf.local.home>
 <20201111182333.GA3249@paulmck-ThinkPad-P72>
 <20201111183430.GN517454@elver.google.com>
 <20201111192123.GB3249@paulmck-ThinkPad-P72>
 <20201111202153.GT517454@elver.google.com>
 <20201112001129.GD3249@paulmck-ThinkPad-P72>
 <CANpmjNNyZs6NrHPmomC4=9MPEvCy1bFA5R2pRsMhG7=c3LhL_Q@mail.gmail.com>
 <20201112161439.GA2989297@elver.google.com>
 <20201112175406.GF3249@paulmck-ThinkPad-P72>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201112175406.GF3249@paulmck-ThinkPad-P72>
User-Agent: Mutt/1.9.4 (2018-02-28)
Precedence: bulk

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);
 		}
 	}