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authorArjan van de Ven <arjan@linux.intel.com>2010-06-17 11:02:15 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-10 13:47:39 -0700
commitd6e679b474c096f1125087e789e7af8886de39d3 (patch)
treeb24235a50fe8c6c7d640999abd02ce6ed5d91cad /drivers/serial
parent68c16b4117cc746a91897d629b61e5f2af18c225 (diff)
downloadlinux-d6e679b474c096f1125087e789e7af8886de39d3.tar.bz2
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>
Diffstat (limited to 'drivers/serial')
-rw-r--r--drivers/serial/mrst_max3110.c46
1 files changed, 18 insertions, 28 deletions
diff --git a/drivers/serial/mrst_max3110.c b/drivers/serial/mrst_max3110.c
index 0341853e0c28..f6ad1ecbff79 100644
--- a/drivers/serial/mrst_max3110.c
+++ b/drivers/serial/mrst_max3110.c
@@ -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;