linux-kernel - Re: [RFC][PATCH 5/14] Introduce union stack

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Message-ID: <20070523132552.GA10067@sergelap.austin.ibm.com>
Date:	Wed, 23 May 2007 08:25:52 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Dickson <paul@...manentmail.com>
Cc:	Badari Pulavarty <pbadari@...ibm.com>, bharata@...ux.vnet.ibm.com,
	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Jan Blunck <j.blunck@...harburg.de>
Subject: Re: [RFC][PATCH  5/14] Introduce union stack

Quoting Paul Dickson (paul@...manentmail.com):
> On Mon, 14 May 2007 13:23:06 -0700, Badari Pulavarty wrote:
> 
> > > +	while (fs) {
> > > +		locked = union_trylock(fs->root);
> > > +		if (!locked)
> > > +			goto loop1;
> > > +		locked = union_trylock(fs->altroot);
> > > +		if (!locked)
> > > +			goto loop2;
> > > +		locked = union_trylock(fs->pwd);
> > > +		if (!locked)
> > > +			goto loop3;
> > > +		break;
> > > +	loop3:
> > > +		union_unlock(fs->altroot);
> > > +	loop2:
> > > +		union_unlock(fs->root);
> > > +	loop1:
> > > +		read_unlock(&fs->lock);
> > > +		UM_DEBUG_LOCK("Failed to get all semaphores in fs_struct!\n");
> > > +		cpu_relax();
> > > +		read_lock(&fs->lock);
> > > +		continue;
> > 
> > Nit.. why "continue" ?
> > 
> > > +	}
> > > +	BUG_ON(!fs);
> 
> How about getting rid of the gotos:
> 
> 	while (fs) {
> 		locked = union_trylock(fs->root);
> 		if (locked) {
> 			locked = union_trylock(fs->altroot);
> 			if (locked) {
> 				locked = union_trylock(fs->pwd);
> 				if (locked)
> 					break;
> 				else {
> 					union_unlock(fs->altroot);
> 					union_unlock(fs->root);
> 				}
> 			else
> 				union_unlock(fs->root);
> 			}
> 		}
> 		read_unlock(&fs->lock);
> 		UM_DEBUG_LOCK("Failed to get all semaphores in fs_struct!\n");
> 		cpu_relax();
> 		read_lock(&fs->lock);
> 	}
> 	BUG_ON(!fs);
> 
> It's the same number of lines.  Shorter if you get rid of the "locked"
> variable.

I dunno, I thought the goto versoin was cleaner and easier to tell that
the right locks are getting unlocked.  The worst part in the second
version is the break in the middle!

-serge
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