Re: [PATCH v4 3/4] iio: ssp_sensors: ssp_spi: use guard() to release mutexes

[Andy Shevchenko]

On Sat, Mar 28, 2026 at 12:24:11PM +0530, Sanjay Chitroda wrote:
> On 26 March 2026 2:52:06 pm IST, Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote:
> >On Thu, Mar 26, 2026 at 01:48:14PM +0530, Sanjay Chitroda wrote:

> >> Replace explicit mutex_lock() and mutex_unlock() with the guard() macro
> >> for cleaner and safer mutex handling.
> >
> >NAK. Please, be very careful when do such changes.

...

> >> -	mutex_unlock(&data->comm_lock);
> >> -
> >
> >Pzzz! See what you are doing here...
> 
> Thank Andy for pointing this out — you’re right, using "guard(mutex)" here
> unintentionally extends the lifetime of "comm_lock" and can hold it across
> the completion wait, which is not safe.
> 
> I’ve reworked the change to keep the original locking semantics intact:
> 
> - "comm_lock" is still explicitly unlocked before "wait_for_completion_timeout()"
> - No sleeping paths are executed while holding "comm_lock"
> - Introduced small helpers to simplify the flow:
>   - "ssp_send_and_enqueue()" for SPI write + pending list add
>   - "ssp_dequeue_msg()" for safe removal from the pending list
> 
> Updated flow looks like this:

If you are going to mix mutex_lock() with guard()(), it's even more NAKish
solution (id est worse than no change).

> This keeps the synchronization boundary unchanged while reducing duplication
> around pending list handling. I’ve also limited "guard()" usage to short,
> local critical sections only.
> 
> Please let me know if you’d prefer keeping the list operations inline instead
> of helpers.

-- 
With Best Regards,
Andy Shevchenko