linux-kernel - Re: [PATCH] Staging: greybus: Fix spinlock

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Date:   Sat, 6 Apr 2019 17:55:55 -0500
From:   Madhumthia Prabakaran <madhumithabiw@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>, johan@...nel.org,
        elder@...nel.org, gregkh@...uxfoundation.org,
        greybus-dev@...ts.linaro.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Staging: greybus: Fix spinlock_t definition without
 comment

On Fri, Apr 05, 2019 at 11:53:04PM +0300, Dan Carpenter wrote:
> On Fri, Apr 05, 2019 at 03:00:46PM -0500, Madhumitha Prabakaran wrote:
> > Fix spinlock_t definition without comment.
> > 
> > Signed-off-by: Madhumitha Prabakaran <madhumithabiw@...il.com>
> > ---
> >  drivers/staging/greybus/connection.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/staging/greybus/connection.h b/drivers/staging/greybus/connection.h
> > index 5ca3befc0636..0aedd246e94a 100644
> > --- a/drivers/staging/greybus/connection.h
> > +++ b/drivers/staging/greybus/connection.h
> > @@ -47,7 +47,7 @@ struct gb_connection {
> >  	unsigned long			flags;
> >  
> >  	struct mutex			mutex;
> > -	spinlock_t			lock;
> > +	spinlock_t			lock; /* Protect structure fields */
> >  	enum gb_connection_state	state;
> 
> What does the mutex do then?  Why can't we just use the spinlock for
> everything?

Here, mutexes protect spinlock_t for gb_connection_state fields and
gb_connection_state fields itself in struct gb_connection.

However, I wasn't sure then and now exactly, how to find out which resources in the
structure, the spinlock or mutex is performing kernel synchronization.

> 
> I did glance at the code and it wasn't immediately obvious to me.

Thanks for reviewing it.

> 
> regards,
> dan carpenter
>