Re: [PATCH v2] counter: ftm-quaddec: use devm_mutex_init()

[William Breathitt Gray <wbg@kernel.org>]

On Wed, May 27, 2026 at 05:57:58PM +0100, Jonathan Cameron wrote:
> On Tue, 26 May 2026 12:24:25 +0200
> Joshua Crofts <joshua.crofts1@gmail.com> wrote:
> 
> > On Mon, 25 May 2026 at 17:14, Stepan Ionichev <sozdayvek@gmail.com> wrote:
> > >
> > > ftm_quaddec_probe() calls mutex_init() but neither the cleanup
> > > action nor a remove callback issues a matching mutex_destroy(),
> > > which leaks the lock debug state when CONFIG_DEBUG_MUTEXES is
> > > enabled.
> > >
> > > Switch to devm_mutex_init() so the mutex is torn down in the same
> > > devm scope it was set up in.
> > >
> > > Fixes: a3b9a99980d9 ("counter: add FlexTimer Module Quadrature decoder counter driver")
> > > Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
> > > ---
> > > v2:
> > > - Add Fixes tag and note that the leak only shows up under
> 
> It's not a leak as such. All that happens is the 'magic' pointer embedded
> in the lock is not set NULL. No memory or counters or anything like that leaked
> in current mainline where the implementation with CONFIG_DEBUG_MUTEXES is
> 
> void mutex_destroy(struct mutex *lock)
> {
> 	DEBUG_LOCKS_WARN_ON(mutex_is_locked(lock));
> 	lock->magic = NULL;
> }

What is the purpose of the magic pointer? Is it just informational, to
catch instances where any attempt to use the mutex occurs after the
device memory is freed for example?

William Breathitt Gray