Messages in this thread | | | Date | Fri, 30 Aug 2013 15:24:45 +0200 | From | Lars-Peter Clausen <> | Subject | Clock framework deadlock with external SPI clockchip |
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Hi,
I'm currently facing a deadlock in the common clock framework that unfortunately is not addressed by the reentrancy patches. I have a external clock chip that is controlled via SPI. So for example to configure the rate of the clock chip you need to send a SPI message. Naturally the clock framework will hold the prepare lock while configuring the rate. Communication in the SPI framework happens asynchronously, spi_sync() will enqueue a message in the SPI masters queue and then wait using wait_for_completion(). The master will call complete() once the transfer has been finished. The SPI master runs in it's own thread in which it processes the messages. In this thread it also calls clk_set_rate() to configure the SPI transfer clock rate based on what the message says. Now the deadlock happens as we try to take the prepare_lock again and since the clock chip and the SPI master run in different threads the reentrancy code does not kick in.
The basic sequence is like this:
=== Clock chip driver === === SPI master driver === clk_prepare_lock() spi_sync() wait_for_completion(X) clk_get_rate() clk_prepare_lock() <--- DEADLOCK clk_prepare_unlock() ... complete(X) ... clk_prepare_unlock()
I'm wondering if you have any idea how this can be fixed. In my opinion we'd need a per clock mutex to address this properly.
Thanks, - Lars
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