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serial: 8250: Clean up the locking for -rt 

In -RT the spin_lock_irqsave() does not spin but sleep if the lock is
taken. Before that, local_irq_save() is invoked which disables
interrupts even on -RT. Therefore local_irq_save() + spin_lock() does not
work.
In the ->sysrq and oops_in_progress case it is save to trylock the lock
i.e. this is what we do now anyway except for ->sysrq where we assume
that the lock is already taken.

The spin_lock_irqsave() grabs the lock and disables the interrupts on
vanilla (the same behavior) and on -RT it won't disable interrupts.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: add a patch description]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This commit is contained in:
Ingo Molnar 2009-07-03 08:30:01 -05:00 committed by Alibek Omarov
parent 29c09674c6
commit 1c81d2eb01
1 changed files with 5 additions and 10 deletions
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15
drivers/tty/serial/8250/8250_core.c
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@ -2882,14 +2882,10 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
touch_nmi_watchdog(); touch_nmi_watchdog();
local_irq_save(flags); if (port->sysrq || oops_in_progress)
if (port->sysrq) { locked = spin_trylock_irqsave(&port->lock, flags);
/* serial8250_handle_irq() already took the lock */ else
locked = 0; spin_lock_irqsave(&port->lock, flags);
} else if (oops_in_progress) {
locked = spin_trylock(&port->lock);
} else
spin_lock(&port->lock);
/* /*
* First save the IER then disable the interrupts * First save the IER then disable the interrupts
@ -2921,8 +2917,7 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
serial8250_modem_status(up); serial8250_modem_status(up);
if (locked) if (locked)
spin_unlock(&port->lock); spin_unlock_irqrestore(&port->lock, flags);
local_irq_restore(flags);
} }
static int __init serial8250_console_setup(struct console *co, char *options) static int __init serial8250_console_setup(struct console *co, char *options)