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

From: Mika Westerberg
Date: Fri Dec 05 2014 - 03:24:54 EST

On Thu, Dec 04, 2014 at 10:01:06PM +0100, Robert Jarzmik wrote:
> Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> 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:
> > 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 ?

When the next message is started pxa2xx_spi_transfer_one_message() gets
called and that will set cur_chip again.
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