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serial_core: Don't re-initialize a previously initialized spinlock.

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The uart_set_options() code unconditionally initalizes the spinlock
on the port. This can cause a deadlock in some situations.

One instance that exposed the problem, was when writing to
/sys/module/kgdboc/parameters/kgdboc to use ttyS0 when the console
is already running on ttyS0. If the spinlock is re-initialized
while the lock is held due to output to the console, there
is a deadlock.

Assume the spinlock is initialized if the port is a console.

Signed-off-by: Randy Witt <rewitt@declaratino.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Randy Witt 2013-10-17 16:56:47 -04:00 committed by Greg Kroah-Hartman
parent dc1ccc4815
commit 42b6a1baa3
1 changed files with 6 additions and 2 deletions
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8
drivers/tty/serial/serial_core.c
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@ -1830,9 +1830,13 @@ uart_set_options(struct uart_port *port, struct console *co,
/*
* Ensure that the serial console lock is initialised
* early.
* If this port is a console, then the spinlock is already
* initialised.
*/
spin_lock_init(&port->lock);
lockdep_set_class(&port->lock, &port_lock_key);
if (!(uart_console(port) && (port->cons->flags & CON_ENABLED))) {
spin_lock_init(&port->lock);
lockdep_set_class(&port->lock, &port_lock_key);
}
memset(&termios, 0, sizeof(struct ktermios));