Commit 40f70c03 authored Nov 16, 2012 by Shinya Kuribayashi Committed by Greg Kroah-Hartman Nov 15, 2012

serial: sh-sci: add locking to console write function to avoid SMP lockup



Symptom:

When entering the suspend with Android logcat running, printk() call
gets stuck and never returns.  The issue can be observed at printk()s
on nonboot CPUs when going to offline with their interrupts disabled,
and never seen at boot CPU (core0 in our case).

Details:

serial_console_write() lacks of appropriate spinlock handling.

In SMP systems, as long as sci_transmit_chars() is being processed
at one CPU core, serial_console_write() can stuck at the other CPU
core(s), when it tries to access to the same serial port _without_
a proper locking.  serial_console_write() waits for the transmit FIFO
getting empty, while sci_transmit_chars() writes data to the FIFO.

In general, peripheral interrupts are routed to boot CPU (core0) by
Linux ARM standard affinity settings.  SCI(F) interrupts are handled
by core0, so sci_transmit_chars() is processed on core0 as well.

When logcat is running, it writes enormous log data to the kernel at
every moment, forever.  So core0 can repeatedly continue to process
sci_transmit_chars() in its interrupt handler, which eventually makes
the other CPU core(s) stuck at serial_console_write().

Looking at serial/8250.c, this is a known console write lockup issue
with SMP kernels.  Fix the sh-sci driver in the same way 8250.c does.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 8c66d6d2

drivers/tty/serial/sh-sci.c

+22 −1

Original line number	Diff line number	Diff line
		@@ -2203,7 +2203,21 @@ static void serial_console_write(struct console co, const char s,
		{
		struct sci_port *sci_port = &sci_ports[co->index];
		struct uart_port *port = &sci_port->port;
		unsigned short bits;
		unsigned short bits, ctrl;
		unsigned long flags;
		int locked = 1;

		local_irq_save(flags);
		if (port->sysrq)
		locked = 0;
		else if (oops_in_progress)
		locked = spin_trylock(&port->lock);
		else
		spin_lock(&port->lock);

		/* first save the SCSCR then disable the interrupts */
		ctrl = serial_port_in(port, SCSCR);
		serial_port_out(port, SCSCR, sci_port->cfg->scscr);

		uart_console_write(port, s, count, serial_console_putchar);

		@@ -2211,6 +2225,13 @@ static void serial_console_write(struct console co, const char s,
		bits = SCxSR_TDxE(port) \| SCxSR_TEND(port);
		while ((serial_port_in(port, SCxSR) & bits) != bits)
		cpu_relax();

		/* restore the SCSCR */
		serial_port_out(port, SCSCR, ctrl);

		if (locked)
		spin_unlock(&port->lock);
		local_irq_restore(flags);
		}

		static int __devinit serial_console_setup(struct console co, char options)

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