linux-kernel - Re: [PATCH] spi/pxa2xx: Clear cur_chip pointer before starting next message

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Message-ID: <87egsfyvsd.fsf@free.fr>
Date:	Thu, 04 Dec 2014 22:01:06 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-spi@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Martin Oldfield <m@...ldfield.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi/pxa2xx: Clear cur_chip pointer before starting next message

Mika Westerberg <mika.westerberg@...ux.intel.com> writes:

> Once the current message is finished, the driver notifies SPI core about
> this by calling spi_finalize_current_message(). This function queues next
> message to be transferred. If there are more messages in the queue, it is
> possible that the driver is asked to transfer the next message at this
> point.
>
> When spi_finalize_current_message() returns the driver clears the
> drv_data->cur_chip pointer to NULL. The problem is that if the driver
> already started the next message clearing drv_data->cur_chip will cause
> NULL pointer dereference which crashes the kernel like:
..zip..
> Fix this by clearing drv_data->cur_chip before we call
> spi_finalize_current_message().

So with your change, we have :
  	drv_data->cur_chip = NULL;
	spi_finalize_current_message(drv_data->master);

In that case, if spi_finalize_current_message() queues another message, upon
this next message completion, won't giveback() be called, and dereference
cur_chip as well ?

Cheers.

--
Robert
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