netdev - Re: [PATCH net] net: dsa: microchip: Added the condition for scheduling ksz_mib_read

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Message-ID: <YWBOeP3dHFbEdg8w@lunn.ch>
Date:   Fri, 8 Oct 2021 15:58:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Arun Ramadoss <arun.ramadoss@...rochip.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        George McCollister <george.mccollister@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        UNGLinuxDriver@...rochip.com,
        Woojung Huh <woojung.huh@...rochip.com>
Subject: Re: [PATCH net] net: dsa: microchip: Added the condition for
 scheduling ksz_mib_read_work

On Fri, Oct 08, 2021 at 02:13:48PM +0530, Arun Ramadoss wrote:
> When the ksz module is installed and removed using rmmod, kernel crashes
> with null pointer dereferrence error. During rmmod, ksz_switch_remove
> function tries to cancel the mib_read_workqueue using
> cancel_delayed_work_sync routine.
> 
> At the end of  mib_read_workqueue execution, it again reschedule the
> workqueue unconditionally. Due to which queue rescheduled after
> mib_interval, during this execution it tries to access dp->slave. But
> the slave is unregistered in the ksz_switch_remove function. Hence
> kernel crashes.

Something not correct here.

https://www.kernel.org/doc/html/latest/core-api/workqueue.html?highlight=delayed_work#c.cancel_delayed_work_sync

This is cancel_work_sync() for delayed works.

and

https://www.kernel.org/doc/html/latest/core-api/workqueue.html?highlight=delayed_work#c.cancel_work_sync

This function can be used even if the work re-queues itself or
migrates to another workqueue.

Maybe the real problem is a missing call to destroy_worker()?

      Andrew