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authorDarren Hart <dvhart@linux.intel.com>2012-06-19 14:00:18 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-07-26 13:37:02 -0700
commit2588aba002d14e938c2f56d299ecf3e7ce1302a5 (patch)
tree872f6a087ce3615b5c8df9f75d255a4d55b713a1 /drivers/tty
parenta7b12929be6cc55eab2dac3330fa9f5984e12dda (diff)
downloadlinux-2588aba002d14e938c2f56d299ecf3e7ce1302a5.tar.bz2
pch_uart: Add eg20t_port lock field, avoid recursive spinlocks
pch_uart_interrupt() takes priv->port.lock which leads to two recursive spinlock calls if low_latency==1 or CONFIG_PREEMPT_RT_FULL=y (one otherwise): pch_uart_interrupt spin_lock_irqsave(priv->port.lock, flags) case PCH_UART_IID_RDR_TO (data ready) handle_rx_to push_rx tty_port_tty_get spin_lock_irqsave(&port->lock, flags) <--- already hold this lock ... tty_flip_buffer_push ... flush_to_ldisc spin_lock_irqsave(&tty->buf.lock) spin_lock_irqsave(&tty->buf.lock) disc->ops->receive_buf(tty, char_buf) n_tty_receive_buf tty->ops->flush_chars() uart_flush_chars uart_start spin_lock_irqsave(&port->lock) <--- already hold this lock Avoid this by using a dedicated lock to protect the eg20t_port structure and IO access to its membase. This is more consistent with the 8250 driver. Ensure priv->lock is always take prior to priv->port.lock when taken at the same time. V2: Remove inadvertent whitespace change. V3: Account for oops_in_progress for the private lock in pch_console_write(). Note: Like the 8250 driver, if a printk is introduced anywhere inside the pch_console_write() critical section, the kernel will hang on a recursive spinlock on the private lock. The oops case is handled by using a trylock in the oops_in_progress case. Signed-off-by: Darren Hart <dvhart@linux.intel.com> CC: Tomoya MORINAGA <tomoya.rohm@gmail.com> CC: Feng Tang <feng.tang@intel.com> CC: Alexander Stein <alexander.stein@systec-electronic.com> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/serial/pch_uart.c38
1 files changed, 26 insertions, 12 deletions
diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index 4fdec6a6b758..d291518a58a4 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -253,6 +253,9 @@ struct eg20t_port {
dma_addr_t rx_buf_dma;
struct dentry *debugfs;
+
+ /* protect the eg20t_port private structure and io access to membase */
+ spinlock_t lock;
};
/**
@@ -1058,7 +1061,7 @@ static irqreturn_t pch_uart_interrupt(int irq, void *dev_id)
int next = 1;
u8 msr;
- spin_lock_irqsave(&priv->port.lock, flags);
+ spin_lock_irqsave(&priv->lock, flags);
handled = 0;
while (next) {
iid = pch_uart_hal_get_iid(priv);
@@ -1116,7 +1119,7 @@ static irqreturn_t pch_uart_interrupt(int irq, void *dev_id)
handled |= (unsigned int)ret;
}
- spin_unlock_irqrestore(&priv->port.lock, flags);
+ spin_unlock_irqrestore(&priv->lock, flags);
return IRQ_RETVAL(handled);
}
@@ -1226,9 +1229,9 @@ static void pch_uart_break_ctl(struct uart_port *port, int ctl)
unsigned long flags;
priv = container_of(port, struct eg20t_port, port);
- spin_lock_irqsave(&port->lock, flags);
+ spin_lock_irqsave(&priv->lock, flags);
pch_uart_hal_set_break(priv, ctl);
- spin_unlock_irqrestore(&port->lock, flags);
+ spin_unlock_irqrestore(&priv->lock, flags);
}
/* Grab any interrupt resources and initialise any low level driver state. */
@@ -1376,7 +1379,8 @@ static void pch_uart_set_termios(struct uart_port *port,
baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);
- spin_lock_irqsave(&port->lock, flags);
+ spin_lock_irqsave(&priv->lock, flags);
+ spin_lock(&port->lock);
uart_update_timeout(port, termios->c_cflag, baud);
rtn = pch_uart_hal_set_line(priv, baud, parity, bits, stb);
@@ -1389,7 +1393,8 @@ static void pch_uart_set_termios(struct uart_port *port,
tty_termios_encode_baud_rate(termios, baud, baud);
out:
- spin_unlock_irqrestore(&port->lock, flags);
+ spin_unlock(&port->lock);
+ spin_unlock_irqrestore(&priv->lock, flags);
}
static const char *pch_uart_type(struct uart_port *port)
@@ -1538,8 +1543,9 @@ pch_console_write(struct console *co, const char *s, unsigned int count)
{
struct eg20t_port *priv;
unsigned long flags;
+ int priv_locked = 1;
+ int port_locked = 1;
u8 ier;
- int locked = 1;
priv = pch_uart_ports[co->index];
@@ -1547,12 +1553,16 @@ pch_console_write(struct console *co, const char *s, unsigned int count)
local_irq_save(flags);
if (priv->port.sysrq) {
- /* serial8250_handle_port() already took the lock */
- locked = 0;
+ spin_lock(&priv->lock);
+ /* serial8250_handle_port() already took the port lock */
+ port_locked = 0;
} else if (oops_in_progress) {
- locked = spin_trylock(&priv->port.lock);
- } else
+ priv_locked = spin_trylock(&priv->lock);
+ port_locked = spin_trylock(&priv->port.lock);
+ } else {
+ spin_lock(&priv->lock);
spin_lock(&priv->port.lock);
+ }
/*
* First save the IER then disable the interrupts
@@ -1570,8 +1580,10 @@ pch_console_write(struct console *co, const char *s, unsigned int count)
wait_for_xmitr(priv, BOTH_EMPTY);
iowrite8(ier, priv->membase + UART_IER);
- if (locked)
+ if (port_locked)
spin_unlock(&priv->port.lock);
+ if (priv_locked)
+ spin_unlock(&priv->lock);
local_irq_restore(flags);
}
@@ -1669,6 +1681,8 @@ static struct eg20t_port *pch_uart_init_port(struct pci_dev *pdev,
pci_enable_msi(pdev);
pci_set_master(pdev);
+ spin_lock_init(&priv->lock);
+
iobase = pci_resource_start(pdev, 0);
mapbase = pci_resource_start(pdev, 1);
priv->mapbase = mapbase;