提交 2588aba0 编写于 作者: D Darren Hart 提交者: Greg Kroah-Hartman

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: NDarren 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: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
上级 a7b12929
......@@ -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;
......
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