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

["Paul E. McKenney" <paulmck@kernel.org>]

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);
 		}
 	}