linux-kernel - Re: [PATCH 1/2] serial: 8250: Initialize pointer to irq

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Date:	Thu, 19 Aug 2010 16:43:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	Michal Simek <monstr@...str.eu>, michal.simek@...alogix.com,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Manuel Lauss <manuel.lauss@...glemail.com>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] serial: 8250: Initialize pointer to irq_info

On Tue, 17 Aug 2010 09:17:20 +0100
Alan Cox <alan@...ux.intel.com> wrote:

> On Tue, 17 Aug 2010 09:59:06 +0200
> Michal Simek <monstr@...str.eu> wrote:
> 
> > Initialize "i" irq_info pointer in serial_unlink_irq_chain.
> > 
> > Compilation warning:
> >   CC      drivers/serial/8250.o
> > drivers/serial/8250.c: In function 'serial8250_shutdown':
> > drivers/serial/8250.c:1701: warning: 'i' may be used uninitialized in
> > this function
> 
> NAK (again)
> 
> Use a newer compiler - modern ones get this right.

: static void serial_unlink_irq_chain(struct uart_8250_port *up)
: {
: 	struct irq_info *i;
: 	struct hlist_node *n;
: 	struct hlist_head *h;
: 
: 	mutex_lock(&hash_mutex);
: 
: 	h = &irq_lists[up->port.irq % NR_IRQ_HASH];
: 
: 	hlist_for_each(n, h) {
: 		i = hlist_entry(n, struct irq_info, node);
: 		if (i->irq == up->port.irq)
: 			break;
: 	}
: 
: 	BUG_ON(n == NULL);
: 	BUG_ON(i->head == NULL);

How can any compiler possibly determine that the hlist_for_each() is
never executed zero times?

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