Re: [PATCH 4.19 053/140] workqueue: Fix spurious sanity check failures in destroy_workqueue()

[Nobuhiro Iwamatsu]

On Mon, Dec 16, 2019 at 06:48:41PM +0100, Greg Kroah-Hartman wrote:
> From: Tejun Heo <tj@xxxxxxxxxx>
> 
> commit def98c84b6cdf2eeea19ec5736e90e316df5206b upstream.
> 
> Before actually destrying a workqueue, destroy_workqueue() checks
> whether it's actually idle.  If it isn't, it prints out a bunch of
> warning messages and leaves the workqueue dangling.  It unfortunately
> has a couple issues.
> 
> * Mayday list queueing increments pwq's refcnts which gets detected as
>   busy and fails the sanity checks.  However, because mayday list
>   queueing is asynchronous, this condition can happen without any
>   actual work items left in the workqueue.
> 
> * Sanity check failure leaves the sysfs interface behind too which can
>   lead to init failure of newer instances of the workqueue.
> 
> This patch fixes the above two by
> 
> * If a workqueue has a rescuer, disable and kill the rescuer before
>   sanity checks.  Disabling and killing is guaranteed to flush the
>   existing mayday list.
> 
> * Remove sysfs interface before sanity checks.
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Reported-by: Marcin Pawlowski <mpawlowski@xxxxxx>
> Reported-by: "Williams, Gerald S" <gerald.s.williams@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 

This commit also requires the following commit:

commit 8efe1223d73c218ce7e8b2e0e9aadb974b582d7f
Author: Tejun Heo <tj@xxxxxxxxxx>
Date:   Fri Sep 20 13:39:57 2019 -0700

    workqueue: Fix missing kfree(rescuer) in destroy_workqueue()

    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Reported-by: Qian Cai <cai@xxxxxx>
    Fixes: def98c84b6cd ("workqueue: Fix spurious sanity check failures in destroy_workqueue()")

This is also required to 4.4, 4.9, 4.14 and 5.3.

Best regards,
  Nobuhiro