serial: earlycon: Add missing spinlock initialization

geertu · gregkh · commit e1dd3bef6d03 · 2015-12-12T23:05:28.000-08:00
If an earlycon console driver needs to acquire the uart_port.lock
spinlock for serial console output, and CONFIG_DEBUG_SPINLOCK=y:

    BUG: spinlock bad magic on CPU#0, swapper/0
     lock: sci_ports+0x0/0x3480, .magic: 00000000, .owner: &lt;none&gt;/-1, .owner_cpu: 0
    CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc2-koelsch-g62ea5edf143bb1d0-dirty #2083
    Hardware name: Generic R8A7791 (Flattened Device Tree)
    [&lt;c00173a0&gt;] (unwind_backtrace) from [&lt;c0013094&gt;] (show_stack+0x10/0x14)
    [&lt;c0013094&gt;] (show_stack) from [&lt;c01f2338&gt;] (dump_stack+0x70/0x8c)
    [&lt;c01f2338&gt;] (dump_stack) from [&lt;c00702d8&gt;] (do_raw_spin_lock+0x20/0x190)
    [&lt;c00702d8&gt;] (do_raw_spin_lock) from [&lt;c0267590&gt;] (serial_console_write+0x4c/0x130)
    [&lt;c0267590&gt;] (serial_console_write) from [&lt;c00734c4&gt;] (call_console_drivers.constprop.13+0xc8/0xec)
    [&lt;c00734c4&gt;] (call_console_drivers.constprop.13) from [&lt;c0074ef0&gt;] (console_unlock+0x354/0x440)
    [&lt;c0074ef0&gt;] (console_unlock) from [&lt;c0075bb4&gt;] (register_console+0x2a0/0x394)
    [&lt;c0075bb4&gt;] (register_console) from [&lt;c06cb750&gt;] (of_setup_earlycon+0x90/0xa4)
    [&lt;c06cb750&gt;] (of_setup_earlycon) from [&lt;c06cfb60&gt;] (setup_of_earlycon+0x118/0x13c)
    [&lt;c06cfb60&gt;] (setup_of_earlycon) from [&lt;c06b34ac&gt;] (do_early_param+0x64/0xb4)
    [&lt;c06b34ac&gt;] (do_early_param) from [&lt;c00472c0&gt;] (parse_args+0x254/0x350)
    [&lt;c00472c0&gt;] (parse_args) from [&lt;c06b3860&gt;] (parse_early_options+0x2c/0x3c)
    [&lt;c06b3860&gt;] (parse_early_options) from [&lt;c06b389c&gt;] (parse_early_param+0x2c/0x40)
    [&lt;c06b389c&gt;] (parse_early_param) from [&lt;c06b5b08&gt;] (setup_arch+0x520/0xaf0)
    [&lt;c06b5b08&gt;] (setup_arch) from [&lt;c06b3948&gt;] (start_kernel+0x94/0x370)
    [&lt;c06b3948&gt;] (start_kernel) from [&lt;40008090&gt;] (0x40008090)

Initialize the spinlock in of_setup_earlycon() and register_earlycon(),
to fix this for both DT-based and legacy earlycon.  If the driver would
reinitialize the spinlock again, this is harmless, as it's allowed to
reinitialize an unlocked spinlock.

Alternatives are:
  - Drivers having an early_serial_console_write() that only performs
    the core functionality of serial_console_write(), without acquiring
    the lock (which may be unsafe, depending on the hardware),
  - Drivers initializing the spinlock in their private earlycon setup
    functions.

As uart_port is owned by generic serial_core, and uart_port.lock is
initialized by uart_add_one_port() for the normal case, this can better
be handled in the earlycon core.

Signed-off-by: Geert Uytterhoeven &lt;geert+renesas@glider.be&gt;
Reviewed-by: Peter Hurley &lt;peter@hurleysoftware.com&gt;
Reported-by: Bjorn Andersson &lt;bjorn.andersson@sonymobile.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
@@ -115,6 +115,7 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
 	if (buf && !parse_options(&early_console_dev, buf))
 		buf = NULL;
 
+	spin_lock_init(&port->lock);
 	port->uartclk = BASE_BAUD * 16;
 	if (port->mapbase)
 		port->membase = earlycon_map(port->mapbase, 64);
@@ -202,6 +203,7 @@ int __init of_setup_earlycon(unsigned long addr,
 	int err;
 	struct uart_port *port = &early_console_dev.port;
 
+	spin_lock_init(&port->lock);
 	port->iotype = UPIO_MEM;
 	port->mapbase = addr;
 	port->uartclk = BASE_BAUD * 16;
