linux-kernel - Re: [PATCH] tty: serial: msm: Fix lock init issue with earlycon

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Message-ID: <544580ED.3050604@hurleysoftware.com>
Date:	Mon, 20 Oct 2014 17:38:53 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Kumar Gala <galak@...eaurora.org>
CC:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH] tty: serial: msm: Fix lock init issue with earlycon

On 10/20/2014 02:27 PM, Stephen Boyd wrote:
> On 10/17/2014 06:13 AM, Kumar Gala wrote:
>> With CONFIG_DEBUG_SPINLOCK enabled we see:
>>
>> BUG: spinlock bad magic on CPU#0, swapper/0
>>   lock: early_console_dev+0x8/0x160, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
>> CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-09733-gb446b33-dirty #18
> 
> [...]
> 
>> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
>> index 4b6c783..8ab27c9 100644
>> --- a/drivers/tty/serial/msm_serial.c
>> +++ b/drivers/tty/serial/msm_serial.c
>> @@ -973,6 +973,8 @@ msm_serial_early_console_setup(struct earlycon_device *device, const char *opt)
>>       if (!device->port.membase)
>>           return -ENODEV;
>>   +    spin_lock_init(&device->port.lock);
>> +
>>       device->con->write = msm_serial_early_write;
>>       return 0;
>>   }
>> @@ -995,6 +997,8 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,
>>       if (!device->port.membase)
>>           return -ENODEV;
>>   +    spin_lock_init(&device->port.lock);
>> +
>>       device->con->write = msm_serial_early_write_dm;
>>       return 0;
>>   }
> 
> Could this be done in the tty core instead?

Or even better: refactor __msm_console_write() so no spin_lock() is required
for the earlycon write.

FWIW, __msm_console_write() is a deadlock-waiting-to_happen since it does
not disable interrupts with spin_lock_irqsave().

Regards,
Peter Hurley
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