linux-kernel - Re: [PATCH] tty: serial: fsl_lpuart: fix del_timer

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Date:   Sat, 3 Dec 2016 15:36:56 +0530
From:   Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
To:     Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Stefan Agner <stefan@...er.ch>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Aaron Brice <aaron.brice@...asoft.com>,
        Nicolae Rosia <nicolae_rosia@...tor.com>,
        <linux-serial@...r.kernel.org>, Chris Healy <cphealy@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: serial: fsl_lpuart: fix del_timer_sync() vs timer
 routine deadlock

On 12/03/2016 02:25 PM, Nikita Yushchenko wrote:

>
> 03.12.2016 10:06, Bhuvanchandra DV пишет:
>> On 12/03/2016 02:58 AM, Nikita Yushchenko wrote:
>>
>>>>> Problem found via lockdep:
>>>>>
>>>>> - lpuart_set_termios() calls del_timer_sync(&sport->lpuart_timer) while
>>>>>     holding sport->port.lock
>>>>>
>>>>> - sport->lpuart_timer routine is lpuart_timer_func() that calls
>>>>>     lpuart_copy_rx_to_tty() that acquires same lock.
>>>>>
>>>>> To fix, move Rx DMA stopping out of lock, as it already is in other
>>>>> places
>>>>> in the same file.
>>>>>
>>>>> While at it, also make Rx DMA start/stop code to look the same is in
>>>>> other places in the same file.
>>>> Yeah I saw that too, never really came around to look closer into it.
>>>>
>>>> Thanks for looking into it.
>>>>
>>>> You removed the check whether there was an old configuration, I think
>>>> the idea of that was that we only resize DMA if it was configured
>>>> differently before...
>>> Per my code reading, checking for sport->lpuart_dma_rx_use should be
>>> enough, this flag will be set only if DMA was previously enabled,
>> The check is to make sure the reconfiguration of DMA is done only when
>> the baudrate is altered.
> Then, ok to use
>
> if (old && sport->lpuart_dma_rx_use) {...}
>
> in both places?

Looks ok to me.

--
Bhuvan