On Fri, Jul 10, 2020 at 03:35:42PM +0200, Greg Kroah-Hartman wrote:

On Fri, Jul 10, 2020 at 03:05:49PM +0300, Cristian Ciocaltea wrote:

quoted

On Fri, May 29, 2020 at 01:34:19PM +0200, Greg Kroah-Hartman wrote:

quoted

On Fri, May 29, 2020 at 02:06:47PM +0300, Cristian Ciocaltea wrote:

quoted

Running a lockdep-enabled kernel leads to the following splat when
probing the owl-uart driver:

[    1.271784] b0124000.serial: ttyOWL2 at MMIO 0xb0124000 (irq = 22, base_baud = 1500000) is a owl-uart
[    1.281226] INFO: trying to register non-static key.
[    1.286179] the code is fine but needs lockdep annotation.
[    1.291648] turning off the locking correctness validator.
[    1.297125] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc7+ #70
[    1.303462] Hardware name: Generic DT based system
[    1.308268] [<80111d3c>] (unwind_backtrace) from [<8010c9b8>] (show_stack+0x10/0x14)
[    1.316003] [<8010c9b8>] (show_stack) from [<805016b4>] (dump_stack+0xb4/0xe0)
[    1.323218] [<805016b4>] (dump_stack) from [<80182dec>] (register_lock_class+0x25c/0x8f4)
[    1.331391] [<80182dec>] (register_lock_class) from [<8017ee34>] (__lock_acquire+0xb4/0x2ee4)
[    1.339901] [<8017ee34>] (__lock_acquire) from [<8018291c>] (lock_acquire+0x424/0x4c8)
[    1.347813] [<8018291c>] (lock_acquire) from [<808597b0>] (_raw_spin_lock_irqsave+0x54/0x68)
[    1.356242] [<808597b0>] (_raw_spin_lock_irqsave) from [<80582e94>] (uart_add_one_port+0x384/0x510)
[    1.365276] [<80582e94>] (uart_add_one_port) from [<8058b4d0>] (owl_uart_probe+0x1bc/0x248)
[    1.373621] [<8058b4d0>] (owl_uart_probe) from [<8059c0e4>] (platform_drv_probe+0x48/0x94)
[    1.381874] [<8059c0e4>] (platform_drv_probe) from [<805997c4>] (really_probe+0x200/0x470)
[    1.390123] [<805997c4>] (really_probe) from [<80599c80>] (driver_probe_device+0x16c/0x1bc)
[    1.398461] [<80599c80>] (driver_probe_device) from [<80599f18>] (device_driver_attach+0x44/0x60)
[    1.407317] [<80599f18>] (device_driver_attach) from [<8059a078>] (__driver_attach+0x144/0x14c)
[    1.416000] [<8059a078>] (__driver_attach) from [<805978ac>] (bus_for_each_dev+0x5c/0xb4)
[    1.424162] [<805978ac>] (bus_for_each_dev) from [<8059896c>] (bus_add_driver+0x118/0x204)
[    1.432410] [<8059896c>] (bus_add_driver) from [<8059ae6c>] (driver_register+0xbc/0xf8)
[    1.440405] [<8059ae6c>] (driver_register) from [<80c1fd24>] (owl_uart_init+0x20/0x40)
[    1.448313] [<80c1fd24>] (owl_uart_init) from [<801021d8>] (do_one_initcall+0x184/0x3a4)
[    1.456399] [<801021d8>] (do_one_initcall) from [<80c01100>] (kernel_init_freeable+0x264/0x2e4)
[    1.465085] [<80c01100>] (kernel_init_freeable) from [<80850a88>] (kernel_init+0x8/0x110)
[    1.473249] [<80850a88>] (kernel_init) from [<80100114>] (ret_from_fork+0x14/0x20)
[    1.480800] Exception stack(0xee8bdfb0 to 0xee8bdff8)
[    1.485841] dfa0:                                     00000000 00000000 00000000 00000000
[    1.494002] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    1.502162] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
[    1.508914] printk: console [ttyOWL2] enabled

The locking issue occurs in uart_configure_port() when trying to
guard the call to set_mctrl().

uart_add_one_port() should normally initialize the spinlock via
uart_port_spin_lock_init(), but it never happens because the port is
detected as a console and, as a consequence, the spinlock is expected
to be already initialized.

The commit a3cb39d258ef
("serial: core: Allow detach and attach serial device for console")
changed the lock initialization logic to assume the spinlock is
initialized even if the console is not enabled.

Therefore, initialize the lock explicitly in owl_uart_probe(), before
attempting to invoke uart_add_one_port().

Fixes: a3cb39d258ef ("serial: core: Allow detach and attach serial device for console")
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
---
 drivers/tty/serial/owl-uart.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
index c149f8c30007..c2fa2f15d50a 100644
--- a/drivers/tty/serial/owl-uart.c
+++ b/drivers/tty/serial/owl-uart.c

@@ -705,6 +705,8 @@ static int owl_uart_probe(struct platform_device *pdev)
 	owl_uart_ports[pdev->id] = owl_port;
 	platform_set_drvdata(pdev, owl_port);
 
+	spin_lock_init(&owl_port->port.lock);
+
 	ret = uart_add_one_port(&owl_uart_driver, &owl_port->port);
 	if (ret)
 		owl_uart_ports[pdev->id] = NULL;

Ugh, another one :(

Thanks for this, will queue this up now.

greg k-h

Hi Greg,

I think this was mistakenly omitted from the inclusion in v5.8, or
has it been postponed for v5.9?

I can't find it anywhere :(

But I think we now have a core fix for this, no need to do this in any
individual driver, right?  Can you test my tty-linus branch to see if
your change is still needed or not?

I was not aware of the alternative approach, at that time Andy
confirmed the expected behaviour is to have a proper initialization
of the spinlock in the driver:
https://lore.kernel.org/lkml/CAHp75Vcz0a87LSnb6Ubt5_bSF3wUcs21GbP119trXER5KBDxbQ@mail.gmail.com/ (local)
https://lore.kernel.org/lkml/CAHp75Vf8xJ2yX-11JsTDnRvZQOK+16aePcB1AUzq=5oO-mFCGQ@mail.gmail.com/ (local)

I have just checked the tty-linus tree and the only related change
seems to be f743061a85f5
("serial: core: Initialise spin lock before use in uart_configure_port()")

I tested it on top of 5.8.0-rc4 and I confirm it fixes the splat,
however I'm a bit confused now regarding the recommended approach since
there is at least one more commit in the tty-linux tree that still 
handles a similar issue in the driver specific code:
f38278e9b810 ("serial: sh-sci: Initialize spinlock for uart console")

Thanks,
Cristi

thanks,

greg k-h

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel