Re: [PATCH V2] mxs/spi: Fix misuse of init_completion

[Chris Ball <cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org>]

Hi Marek,

On Thu, Aug 23 2012, Marek Vasut wrote:
> The init_completion() call does reinit not only the variable carrying
> the flag that the completion finished, but also initialized the
> waitqueue associated with the completion. On the contrary, the
> INIT_WAITQUEUE() call only reinits the flag.
>
> In case there was anything still stuck in the waitqueue, subsequent call
> to init_completion() would be able to create possible race condition. This
> patch uses the proper function and moves init_completion() into .probe() call
> of the driver, to be issued only once.
>
> Note that such scenario is impossible, since two threads can never enter the
> mxs_spi_txrx_dma(), since whole this section is protected by mutex in SPI core.
> This by no means allows this issue to exit though.
>
> Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>

Thanks for writing that up -- I appreciate seeing the explanation of the
problems this could have caused.

- Chris.
-- 
Chris Ball   <cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org>   <http://printf.net/>
One Laptop Per Child

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