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

From: Robert Jarzmik
Date: Thu Dec 04 2014 - 16:01:15 EST

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;

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 ?


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