From 2588aba002d14e938c2f56d299ecf3e7ce1302a5 Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Tue, 19 Jun 2012 14:00:18 -0700 Subject: [PATCH] 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 CC: Tomoya MORINAGA CC: Feng Tang CC: Alexander Stein Acked-by: Alan Cox Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/pch_uart.c | 38 ++++++++++++++++++++++++++------------ 1 file changed, 26 insertions(+), 12 deletions(-) diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c index 4fdec6a6..d291518 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; -- 2.7.4