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: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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@ -48,6 +48,10 @@
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#define PR_FMT "mrst_max3110: "
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#define UART_TX_NEEDED 1
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#define CON_TX_NEEDED 2
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#define BIT_IRQ_PENDING 3
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struct uart_max3110 {
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struct uart_port port;
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struct spi_device *spi;
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@ -63,15 +67,13 @@ struct uart_max3110 {
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u8 clock;
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u8 parity, word_7bits;
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atomic_t uart_tx_need;
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unsigned long uart_flags;
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/* console related */
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struct circ_buf con_xmit;
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atomic_t con_tx_need;
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/* irq related */
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u16 irq;
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atomic_t irq_pending;
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};
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/* global data structure, may need be removed */
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@ -176,10 +178,9 @@ static void serial_m3110_con_putchar(struct uart_port *port, int ch)
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xmit->head = (xmit->head + 1) & (PAGE_SIZE - 1);
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}
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if (!atomic_read(&max->con_tx_need)) {
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atomic_set(&max->con_tx_need, 1);
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if (!test_and_set_bit(CON_TX_NEEDED, &max->uart_flags))
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wake_up_process(max->main_thread);
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}
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}
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/*
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@ -318,10 +319,8 @@ static void serial_m3110_start_tx(struct uart_port *port)
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struct uart_max3110 *max =
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container_of(port, struct uart_max3110, port);
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if (!atomic_read(&max->uart_tx_need)) {
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atomic_set(&max->uart_tx_need, 1);
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if (!test_and_set_bit(UART_TX_NEEDED, &max->uart_flags))
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wake_up_process(max->main_thread);
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}
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}
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static void receive_chars(struct uart_max3110 *max, unsigned char *str, int len)
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@ -392,32 +391,23 @@ static int max3110_main_thread(void *_max)
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pr_info(PR_FMT "start main thread\n");
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do {
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wait_event_interruptible(*wq, (atomic_read(&max->irq_pending) ||
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atomic_read(&max->con_tx_need) ||
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atomic_read(&max->uart_tx_need)) ||
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kthread_should_stop());
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wait_event_interruptible(*wq, max->uart_flags || kthread_should_stop());
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mutex_lock(&max->thread_mutex);
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#ifdef CONFIG_MRST_MAX3110_IRQ
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if (atomic_read(&max->irq_pending)) {
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if (test_and_clear_bit(BIT_IRQ_PENDING, &max->uart_flags))
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max3110_console_receive(max);
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atomic_set(&max->irq_pending, 0);
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}
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#endif
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/* first handle console output */
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if (atomic_read(&max->con_tx_need)) {
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if (test_and_clear_bit(CON_TX_NEEDED, &max->uart_flags))
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send_circ_buf(max, xmit);
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atomic_set(&max->con_tx_need, 0);
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}
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/* handle uart output */
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if (atomic_read(&max->uart_tx_need)) {
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if (test_and_clear_bit(UART_TX_NEEDED, &max->uart_flags))
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transmit_char(max);
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atomic_set(&max->uart_tx_need, 0);
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}
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mutex_unlock(&max->thread_mutex);
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} while (!kthread_should_stop());
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return ret;
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@ -430,10 +420,9 @@ static irqreturn_t serial_m3110_irq(int irq, void *dev_id)
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/* max3110's irq is a falling edge, not level triggered,
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* so no need to disable the irq */
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if (!atomic_read(&max->irq_pending)) {
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atomic_inc(&max->irq_pending);
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if (!test_and_set_bit(BIT_IRQ_PENDING, &max->uart_flags))
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wake_up_process(max->main_thread);
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}
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return IRQ_HANDLED;
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}
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#else
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@ -753,7 +742,8 @@ static int serial_m3110_probe(struct spi_device *spi)
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max->baud = 0;
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max->cur_conf = 0;
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atomic_set(&max->irq_pending, 0);
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max->uart_flags = 0;
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/* Check if reading configuration register returns something sane */
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res = RC_TAG;
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