linux-kernel - Re: [PATCH] staging: sm750fb: move common locking code to a macro

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Date:   Wed, 21 Jun 2017 10:59:01 +0200
From:   Dhananjay Balan <mail@...lan.in>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     sudipm.mukherjee@...il.com, devel@...verdev.osuosl.org,
        linux-fbdev@...r.kernel.org, teddy.wang@...iconmotion.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: sm750fb: move common locking code to a macro

Tue, 2017-06-20, 23:05 +0300-യ്ക്ക, Dan Carpenter എഴുതിയിരിക്കുന്നു:
> On Tue, Jun 20, 2017 at 06:50:13PM +0200, Dhananjay Balan wrote:
> > The locking and unlocking code used by copy routines is common, so
> > moved it to a macro.
> > 
> > Signed-off-by: Dhananjay Balan <mail@...lan.in>
> > ---
> >  drivers/staging/sm750fb/sm750.c | 81 ++++++++++++++++-------------
> > ------------
> >  1 file changed, 31 insertions(+), 50 deletions(-)
> > 
> > diff --git a/drivers/staging/sm750fb/sm750.c
> > b/drivers/staging/sm750fb/sm750.c
> > index 386d4adcd91d..d8ab83aea46d 100644
> > --- a/drivers/staging/sm750fb/sm750.c
> > +++ b/drivers/staging/sm750fb/sm750.c
> > @@ -156,12 +156,25 @@ static int lynxfb_ops_cursor(struct fb_info
> > *info, struct fb_cursor *fbcursor)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * If not using spin_lock, system will die if user frequently
> > loads and
> > + * immediately unloads driver (dual)
> > + */
> > +#define dual_safe_call(func, ...)					
> > \
> > +	do {							
> > 	\
> > +		if (sm750_dev->fb_count > 1)			
> > 	\
> > +			spin_lock(&sm750_dev->slock);		
> > 	\
> > +		func(__VA_ARGS__);					
> > \
> > +		if (sm750_dev->fb_count > 1)			
> > 	\
> > +			spin_unlock(&sm750_dev->slock);		
> > 	\
> > +	} while (0)
> > +
> 
> I feel like this is the wrong approach.  You could just make a small
> lock function and a small unlock function.  Except that if statement
> seems kind of bogus.  What happens if ->fb_count is 0 when we lock
> and
> 1 when we unlock?  Why not lock unconditionally?  It is not likely to
> be
> contested if there are no other users.
I've to admit that I don't have much info, but is fb_count supposed to
change during this execution?
> 
> >  static void lynxfb_ops_fillrect(struct fb_info *info,
> >  				const struct fb_fillrect *region)
> >  {
> >  	struct lynxfb_par *par;
> >  	struct sm750_dev *sm750_dev;
> > -	unsigned int base, pitch, Bpp, rop;
> > +	unsigned int base, pitch, bit_pp, rop;
> 
> This part has nothing to do with locking...  *frowny face*
Sorry about that, I'll split this into separate commit.


Thanks,
Dhananjay Balan.