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

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Message-ID: <68d2fd35-834b-fe74-c9a2-719c7b62a83a@cogentembedded.com>
Date:   Sat, 3 Dec 2016 11:55:41 +0300
From:   Nikita Yushchenko <nikita.yoush@...entembedded.com>
To:     Bhuvanchandra DV <bhuvanchandra.dv@...adex.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



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?