Re: [PATCH 15/78] ASoC: codecs: cs42l43: Use guard() for mutex locks

[David Laight <david.laight.linux@gmail.com>]

On Fri, 19 Jun 2026 15:20:37 +0700
Bui Duc Phuc <phucduc.bui@gmail.com> wrote:

> Hi Charles, David,
> 
> Thanks for the review.
> 
> > >
> > > I believe you have to use scoped_guard here, as there is a return
> > > from the function above, if memory serves it attempts to release
> > > the mutex on that path despite it being above the guard.  
> >
> > Indeed.
> > I believe clang will complain.
> > That makes these mechanical conversions of existing code dangerous churn.
> >
> > While using guard() (etc) can make it easier to ensure the lock is released
> > when functions have multiple error exits, I'm not convinced it makes the
> > code any easier to read (other people may disagree).
> >  
> 
> I built the code with both GCC and Clang and didn't see any warnings.
> 
> My understanding was that the early return exits the function before
> the guard is instantiated, so it should not affect the guard's cleanup
> handling.
> 
> Could you explain what issue you are referring to? I may be missing
> something.

When a variable is defined (and initialised) part way down a block the
compiler moves the definition to the top of the block but doesn't initialise
it at all, the first assignment happens where the code contains the
definition.

However the destructor is always called at the end of the block.
So if you return from a function before the definition the destructor
is called with an uninitialised argument.

This has always been a problem with C++.
It usually happens when you define a variable inside a switch statement.

	David

> 
> Best regards,
> Phuc