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serial: fix wakup races in the mrst_max3110 driver

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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>
This commit is contained in:
Arjan van de Ven 2010-06-17 11:02:15 +01:00 committed by Greg Kroah-Hartman
parent 68c16b4117
commit d6e679b474
1 changed files with 18 additions and 28 deletions
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46
drivers/serial/mrst_max3110.c
View File

@ -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 */
@ -176,10 +178,9 @@ 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);
}
}
/*
@ -318,10 +319,8 @@ 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;