RE: AW: [PATCH] soc: aspeed: fix a ternary sign expansion bug

From: David Laight <David.Laight@ACULAB.COM>
To: 'Sergey Organov' <sorganov@gmail.com>, Walter Harms <wharms@bfs.de>
Cc: 'Dan Carpenter' <dan.carpenter@oracle.com>,
	Joel Stanley <joel@jms.id.au>, Andrew Jeffery <andrew@aj.id.au>,
	"Chia-Wei, Wang" <chiawei_wang@aspeedtech.com>,
	Jae Hyun Yoo <jae.hyun.yoo@intel.com>,
	"John Wang" <wangzhiqiang.bj@bytedance.com>,
	Brad Bishop <bradleyb@fuzziesquirrel.com>,
	Patrick Venture <venture@google.com>,
	Benjamin Fair <benjaminfair@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Robert Lippert <rlippert@google.com>,
	"linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-janitors@vger.kernel.org"
	<kernel-janitors@vger.kernel.org>
Subject: RE: AW: [PATCH] soc: aspeed: fix a ternary sign expansion bug
Date: Fri, 23 Apr 2021 14:55:29 +0000	[thread overview]
Message-ID: <635275613c384fe381df4ae4ac30f380@AcuMS.aculab.com> (raw)
In-Reply-To: <878s59rrn0.fsf@osv.gnss.ru>

From: Sergey Organov
> Sent: 23 April 2021 15:40
> 
> Walter Harms <wharms@bfs.de> writes:
> 
> > as indepentent observer,
> > i would go for Dans solution:
> >
> > ret = kfifo_to_user();
> > /* if an error occurs just return */
> > if (ret)
> >    return ret;
> >
> > /* otherwise return the copied number of bytes */
> >
> > return copied;
> >
> > there is no need for any deeper language knowledge,
> 
> Yep, but this is not idiomatic C, so one looking at this code would
> tend to convert it back to ternary, and the actual problem here is that
> the type of 'copied' does not match the return type of the function.

Actually changing the type of 'ret' to ssize_t is probably
the safest change.

That works until someone tries to optimise out 'ret' by doing:

	return kfifo_to_user(...) ?: count;

Or rattle through and remove the 'pass by reference' 'count'
parameter from kfifo_to_user() in favour of returning the
value the callers want.

I need to stop looking at this code :-)

	David

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