Re: [patch V3 17/17] Bluetooth: hci_qca: Fix the teardown problem for real - Anna-Maria Behnsen

From: Anna-Maria Behnsen <anna-maria@linutronix.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Guenter Roeck <linux@roeck-us.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Julia Lawall <Julia.Lawall@inria.fr>,
	Arnd Bergmann <arnd@arndb.de>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Marc Zyngier <maz@kernel.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	linux-bluetooth@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	netdev@vger.kernel.org, Jacob Keller <jacob.e.keller@intel.com>
Subject: Re: [patch V3 17/17] Bluetooth: hci_qca: Fix the teardown problem for real
Date: Thu, 24 Nov 2022 14:56:35 +0100 (CET)	[thread overview]
Message-ID: <21108e77-f67d-528-dd61-249c5ebe217f@linutronix.de> (raw)
In-Reply-To: <20221123201625.435907114@linutronix.de>

On Wed, 23 Nov 2022, Thomas Gleixner wrote:

> While discussing solutions for the teardown problem which results from
> circular dependencies between timers and workqueues, where timers schedule
> work from their timer callback and workqueues arm the timers from work
> items, it was discovered that the recent fix to the QCA code is incorrect.
> 
> That commit fixes the obvious problem of using del_timer() instead of
> del_timer_sync() and reorders the teardown calls to
> 
>    destroy_workqueue(wq);
>    del_timer_sync(t);
> 
> This makes it less likely to explode, but it's still broken:
> 
>    destroy_workqueue(wq);
>    /* After this point @wq cannot be touched anymore */
> 
>    ---> timer expires
>          queue_work(wq) <---- Results in a NULl pointer dereference

The last NIT (for now...): s/NULl/NULL

Thanks,

	Anna-Maria