Commit d6e679b4 authored by Arjan van de Ven's avatar Arjan van de Ven Committed by Greg Kroah-Hartman
Browse files

serial: fix wakup races in the mrst_max3110 driver 



The mrst_max3110 driver had a set of unsafe wakeup sequences
along the following line:

if (!atomic_read(&foo)) {
  atomic_set(&foo, 1);
  wake_up(worker_thread);
}
and the worker thread would do

if (atomic_read(&foo)) {
  do_work();
  atomic_set(&foo, 0);
}

which can result in various missed wakups due to test-then-set races,
as well as due to clear-after-work instead of clear-before-work.

This patch fixes these races by using the proper bit test-and-set operations,
and by doing clear-before-work.

Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 68c16b41

drivers/serial/mrst_max3110.c

+18 −28
Original line number Diff line number Diff line
@@ -48,6 +48,10 @@ 


#define PR_FMT	"mrst_max3110: "



#define UART_TX_NEEDED 1

#define CON_TX_NEEDED  2

#define BIT_IRQ_PENDING    3



struct uart_max3110 {

	struct uart_port port;

	struct spi_device *spi;
@@ -63,15 +67,13 @@ struct uart_max3110 { 
	u8 clock;

	u8 parity, word_7bits;



	atomic_t uart_tx_need;

	unsigned long uart_flags;



	/* console related */

	struct circ_buf con_xmit;

	atomic_t con_tx_need;



	/* irq related */

	u16 irq;

	atomic_t irq_pending;

};



/* global data structure, may need be removed */
@@ -176,11 +178,10 @@ static void serial_m3110_con_putchar(struct uart_port *port, int ch) 
		xmit->head = (xmit->head + 1) & (PAGE_SIZE - 1);

	}



	if (!atomic_read(&max->con_tx_need)) {

		atomic_set(&max->con_tx_need, 1);



	if (!test_and_set_bit(CON_TX_NEEDED, &max->uart_flags))

		wake_up_process(max->main_thread);

}

}



/*

 * Print a string to the serial port trying not to disturb
@@ -318,11 +319,9 @@ static void serial_m3110_start_tx(struct uart_port *port) 
	struct uart_max3110 *max =

		container_of(port, struct uart_max3110, port);



	if (!atomic_read(&max->uart_tx_need)) {

		atomic_set(&max->uart_tx_need, 1);

	if (!test_and_set_bit(UART_TX_NEEDED, &max->uart_flags))

		wake_up_process(max->main_thread);

}

}



static void receive_chars(struct uart_max3110 *max, unsigned char *str, int len)

{
@@ -392,32 +391,23 @@ static int max3110_main_thread(void *_max) 
	pr_info(PR_FMT "start main thread\n");



	do {

		wait_event_interruptible(*wq, (atomic_read(&max->irq_pending) ||

					       atomic_read(&max->con_tx_need) ||

					     atomic_read(&max->uart_tx_need)) ||

					     kthread_should_stop());

		wait_event_interruptible(*wq, max->uart_flags || kthread_should_stop());



		mutex_lock(&max->thread_mutex);



#ifdef CONFIG_MRST_MAX3110_IRQ

		if (atomic_read(&max->irq_pending)) {

		if (test_and_clear_bit(BIT_IRQ_PENDING, &max->uart_flags))

			max3110_console_receive(max);

			atomic_set(&max->irq_pending, 0);

		}

#endif



		/* first handle console output */

		if (atomic_read(&max->con_tx_need)) {

		if (test_and_clear_bit(CON_TX_NEEDED, &max->uart_flags))

			send_circ_buf(max, xmit);

			atomic_set(&max->con_tx_need, 0);

		}



		/* handle uart output */

		if (atomic_read(&max->uart_tx_need)) {

		if (test_and_clear_bit(UART_TX_NEEDED, &max->uart_flags))

			transmit_char(max);

			atomic_set(&max->uart_tx_need, 0);

		}



		mutex_unlock(&max->thread_mutex);



	} while (!kthread_should_stop());



	return ret;
@@ -430,10 +420,9 @@ static irqreturn_t serial_m3110_irq(int irq, void *dev_id) 


	/* max3110's irq is a falling edge, not level triggered,

	 * so no need to disable the irq */

	if (!atomic_read(&max->irq_pending)) {

		atomic_inc(&max->irq_pending);

	if (!test_and_set_bit(BIT_IRQ_PENDING, &max->uart_flags))

		wake_up_process(max->main_thread);

	}



	return IRQ_HANDLED;

}

#else
@@ -753,7 +742,8 @@ static int serial_m3110_probe(struct spi_device *spi) 
	max->baud = 0;



	max->cur_conf = 0;

	atomic_set(&max->irq_pending, 0);

	max->uart_flags = 0;



	/* Check if reading configuration register returns something sane */



	res = RC_TAG;

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