linux-kernel - Re: [PATCHv2] serial: 8250: change lock order in serial8250_do

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Message-ID: <20200819092106.GA4353@alley>
Date:   Wed, 19 Aug 2020 11:21:06 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Tony Lindgren <tony@...mide.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Raul Rangel <rrangel@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-serial@...r.kernel.org
Subject: Re: [PATCHv2] serial: 8250: change lock order in
 serial8250_do_startup()

On Mon 2020-08-17 11:26:46, Sergey Senozhatsky wrote:
> We have a number of "uart.port->desc.lock vs desc.lock->uart.port"
> lockdep reports coming from 8250 driver; this causes a bit of trouble
> to people, so let's fix it.
> 
> The problem is reverse lock order in two different call paths:
> 
> chain #1:
> 
>  serial8250_do_startup()
>   spin_lock_irqsave(&port->lock);
>    disable_irq_nosync(port->irq);
>     raw_spin_lock_irqsave(&desc->lock)
> 
> chain #2:
> 
>   __report_bad_irq()
>    raw_spin_lock_irqsave(&desc->lock)
>     for_each_action_of_desc()
>      printk()
>       spin_lock_irqsave(&port->lock);
> 
> Fix this by changing the order of locks in serial8250_do_startup():
>  do disable_irq_nosync() first, which grabs desc->lock, and grab
>  uart->port after that, so that chain #1 and chain #2 have same lock
>  order.
> 
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

The patch is committed in printk/linux.git, branch for-5.10.

Best Regards,
Petr