From: Dan Carpenter <dan.carpenter@oracle.com>
To: Sergey Organov <sorganov@gmail.com>
Cc: David Laight <David.Laight@ACULAB.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: [PATCH] soc: aspeed: fix a ternary sign expansion bug
Date: Fri, 23 Apr 2021 14:14:26 +0300 [thread overview]
Message-ID: <20210423111425.GT1959@kadam> (raw)
In-Reply-To: <877dktuvmz.fsf@osv.gnss.ru>
On Fri, Apr 23, 2021 at 01:45:40PM +0300, Sergey Organov wrote:
> David Laight <David.Laight@ACULAB.COM> writes:
>
> > From: Dan Carpenter
> >> Sent: 22 April 2021 10:12
> >>
> >> The intent here was to return negative error codes but it actually
> >> returns positive values. The problem is that type promotion with
> >> ternary operations is quite complicated.
> >>
> >> "ret" is an int. "copied" is a u32. And the snoop_file_read() function
> >> returns long. What happens is that "ret" is cast to u32 and becomes
> >> positive then it's cast to long and it's still positive.
> >>
> >> Fix this by removing the ternary so that "ret" is type promoted directly
> >> to long.
> >>
> >> Fixes: 3772e5da4454 ("drivers/misc: Aspeed LPC snoop output using misc chardev")
> >> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> >> ---
> >> drivers/soc/aspeed/aspeed-lpc-snoop.c | 4 +++-
> >> 1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> index 210455efb321..eceeaf8dfbeb 100644
> >> --- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> +++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> @@ -94,8 +94,10 @@ static ssize_t snoop_file_read(struct file *file, char __user *buffer,
> >> return -EINTR;
> >> }
> >> ret = kfifo_to_user(&chan->fifo, buffer, count, &copied);
> >> + if (ret)
> >> + return ret;
> >>
> >> - return ret ? ret : copied;
> >> + return copied;
> >
> > I wonder if changing it to:
> > return ret ? ret + 0L : copied;
> >
> > Might make people think in the future and not convert it back
> > as an 'optimisation'.
>
> It rather made me think: "what the heck is going on here?!"
>
> Shouldn't it better be:
>
> return ret ? ret : (long)copied;
>
> or even:
>
> return ret ?: (long)copied;
I work with Greg a lot and his bias against ternaries has rubbed off a
bit. They're sort of Perl-ish. And I have nothing against Perl. It's
a perfectly fine programming language, but when I write Perl I write it
in C.
regards,
dan carpenter
prev parent reply other threads:[~2021-04-23 11:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 9:11 [PATCH] soc: aspeed: fix a ternary sign expansion bug Dan Carpenter
2021-04-22 9:24 ` Al Viro
2021-04-22 9:26 ` Al Viro
2021-04-22 14:56 ` Patrick Venture
2021-04-22 16:21 ` David Laight
2021-04-23 0:07 ` Joel Stanley
2021-04-23 7:43 ` Dan Carpenter
2021-04-23 10:45 ` Sergey Organov
2021-04-23 10:54 ` David Laight
2021-04-23 11:03 ` AW: " Walter Harms
2021-04-23 14:40 ` Sergey Organov
2021-04-23 14:55 ` David Laight
2021-04-23 15:24 ` Dan Carpenter
2021-04-23 11:14 ` Dan Carpenter [this message]
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