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tty: serial: fsl_lpuart: lock port on console write 

The console write code is not entirely race free (e.g. the operations
to disabling the UART interrupts are not atomic) hence locking is
required. This has been become apparent with the PREEMPT RT patchset
applied: With the fully preemptible kernel configuration the system
often ended up in a freeze already at startup.

Disable interrupts and lock using read_lock_irqsave. Try to lock in
the sysrq/oops case, but don't bother if locking fails.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stefan Agner 2017-03-24 11:33:46 -07:00 committed by Greg Kroah-Hartman
parent 4d9d7d896d
commit abf1e0a980
1 changed files with 20 additions and 0 deletions
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20
drivers/tty/serial/fsl_lpuart.c
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@ -1705,6 +1705,13 @@ lpuart_console_write(struct console *co, const char *s, unsigned int count)
{
struct lpuart_port *sport = lpuart_ports[co->index];
unsigned char old_cr2, cr2;
unsigned long flags;
int locked = 1;
if (sport->port.sysrq || oops_in_progress)
locked = spin_trylock_irqsave(&sport->port.lock, flags);
else
spin_lock_irqsave(&sport->port.lock, flags);
/* first save CR2 and then disable interrupts */
cr2 = old_cr2 = readb(sport->port.membase + UARTCR2);
@ -1719,6 +1726,9 @@ lpuart_console_write(struct console *co, const char *s, unsigned int count)
barrier();
writeb(old_cr2, sport->port.membase + UARTCR2);
if (locked)
spin_unlock_irqrestore(&sport->port.lock, flags);
}
static void
@ -1726,6 +1736,13 @@ lpuart32_console_write(struct console *co, const char *s, unsigned int count)
{
struct lpuart_port *sport = lpuart_ports[co->index];
unsigned long old_cr, cr;
unsigned long flags;
int locked = 1;
if (sport->port.sysrq || oops_in_progress)
locked = spin_trylock_irqsave(&sport->port.lock, flags);
else
spin_lock_irqsave(&sport->port.lock, flags);
/* first save CR2 and then disable interrupts */
cr = old_cr = lpuart32_read(sport->port.membase + UARTCTRL);
@ -1740,6 +1757,9 @@ lpuart32_console_write(struct console *co, const char *s, unsigned int count)
barrier();
lpuart32_write(old_cr, sport->port.membase + UARTCTRL);
if (locked)
spin_unlock_irqrestore(&sport->port.lock, flags);
}
/*