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dmaengine: virt-dma: Support for race free transfer termination 

Even with the introduced vchan_synchronize() we can face race when
terminating a cyclic transfer.

If the terminate_all is called after the interrupt handler called
vchan_cyclic_callback(), but before the vchan_complete tasklet is called:
vc->cyclic is set to the cyclic descriptor, but the descriptor itself was
freed up in the driver's terminate_all() callback.
When the vhan_complete() is executed it will try to fetch the vc->cyclic
vdesc, but the pointer is pointing now to uninitialized memory leading to
(hard to reproduce) kernel crash.

In order to fix this, drivers should:
- call vchan_terminate_vdesc() from their terminate_all callback instead
calling their free_desc function to free up the descriptor.
- implement device_synchronize callback and call vchan_synchronize().

This way we can make sure that the descriptor is only going to be freed up
after the vchan_callback was executed in a safe manner.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
This commit is contained in:
Peter Ujfalusi 2017-11-14 16:32:04 +02:00 committed by Vinod Koul
parent 6af149d2b1
commit 1c7f072d94
1 changed files with 30 additions and 0 deletions
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30
drivers/dma/virt-dma.h
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@ -35,6 +35,7 @@ struct virt_dma_chan {
struct list_head desc_completed;
struct virt_dma_desc *cyclic;
struct virt_dma_desc *vd_terminated;
};
static inline struct virt_dma_chan *to_virt_chan(struct dma_chan *chan)
@ -129,6 +130,25 @@ static inline void vchan_cyclic_callback(struct virt_dma_desc *vd)
tasklet_schedule(&vc->task);
}
/**
* vchan_terminate_vdesc - Disable pending cyclic callback
* @vd: virtual descriptor to be terminated
*
* vc.lock must be held by caller
*/
static inline void vchan_terminate_vdesc(struct virt_dma_desc *vd)
{
struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
/* free up stuck descriptor */
if (vc->vd_terminated)
vchan_vdesc_fini(vc->vd_terminated);
vc->vd_terminated = vd;
if (vc->cyclic == vd)
vc->cyclic = NULL;
}
/**
* vchan_next_desc - peek at the next descriptor to be processed
* @vc: virtual channel to obtain descriptor from
@ -182,10 +202,20 @@ static inline void vchan_free_chan_resources(struct virt_dma_chan *vc)
* Makes sure that all scheduled or active callbacks have finished running. For
* proper operation the caller has to ensure that no new callbacks are scheduled
* after the invocation of this function started.
* Free up the terminated cyclic descriptor to prevent memory leakage.
*/
static inline void vchan_synchronize(struct virt_dma_chan *vc)
{
unsigned long flags;
tasklet_kill(&vc->task);
spin_lock_irqsave(&vc->lock, flags);
if (vc->vd_terminated) {
vchan_vdesc_fini(vc->vd_terminated);
vc->vd_terminated = NULL;
}
spin_unlock_irqrestore(&vc->lock, flags);
}
#endif