at_hdmac does not release lock before the callback - deadlock · Jouko Haapaluoma <hidden> · 2014-01-27
at_hdmac does not release lock before the callback - deadlock · Jouko Haapaluoma <hidden> · 2014-01-27
[RFC PATCH 0/2] dmaengine: at_hdmac: fix locking according to slave DMA requirements · Nicolas Ferre <hidden> · 2014-01-27
[PATCH 1/2] dmaengine: at_hdmac: remove the call to issue_pending from tx_status · Nicolas Ferre <hidden> · 2014-01-27
[PATCH 2/2] dmaengine: at_hdmac: run callback function with no lock held nor interrupts disabled · Nicolas Ferre <hidden> · 2014-01-27
Re: [PATCH 2/2] dmaengine: at_hdmac: run callback function with no lock held nor interrupts disabled · Vinod Koul <hidden> · 2014-03-11
RE: [RFC PATCH 0/2] dmaengine: at_hdmac: fix locking according to slave DMA requirements · Jouko Haapaluoma <hidden> · 2014-01-31

at_hdmac does not release lock before the callback - deadlock

From: Jouko Haapaluoma <hidden>
Date: 2014-01-27 14:12:28

After further investigation it seems that the deadlocks  would happen only when CONFIG_SMP is enabled or RT_PREEMPT patch is used. When CONFIG_SMP or RT_PREEMPT is not used, the spinlocks will only disable preemption which does not cause a deadlock. However, with the CONFIG_SMP or the RT_PREEMPT patch spinlocks are actual locks and deadlocks can occur.

This might explain why this problem hasn't been noticed before. At least the Atmel serial driver from linux4sam git causes deadlocks with the RT_PREEMPT because of this issue. 

BR,
Jouko Haapaluoma

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