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>
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@ -35,6 +35,7 @@ struct virt_dma_chan {
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struct list_head desc_completed;
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struct virt_dma_desc *cyclic;
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struct virt_dma_desc *vd_terminated;
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};
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static inline struct virt_dma_chan *to_virt_chan(struct dma_chan *chan)
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@ -129,6 +130,25 @@ static inline void vchan_cyclic_callback(struct virt_dma_desc *vd)
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tasklet_schedule(&vc->task);
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}
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/**
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* vchan_terminate_vdesc - Disable pending cyclic callback
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* @vd: virtual descriptor to be terminated
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*
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* vc.lock must be held by caller
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*/
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static inline void vchan_terminate_vdesc(struct virt_dma_desc *vd)
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{
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struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
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/* free up stuck descriptor */
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if (vc->vd_terminated)
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vchan_vdesc_fini(vc->vd_terminated);
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vc->vd_terminated = vd;
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if (vc->cyclic == vd)
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vc->cyclic = NULL;
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}
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/**
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* vchan_next_desc - peek at the next descriptor to be processed
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* @vc: virtual channel to obtain descriptor from
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@ -182,10 +202,20 @@ static inline void vchan_free_chan_resources(struct virt_dma_chan *vc)
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* Makes sure that all scheduled or active callbacks have finished running. For
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* proper operation the caller has to ensure that no new callbacks are scheduled
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* after the invocation of this function started.
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* Free up the terminated cyclic descriptor to prevent memory leakage.
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*/
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static inline void vchan_synchronize(struct virt_dma_chan *vc)
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{
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unsigned long flags;
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tasklet_kill(&vc->task);
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spin_lock_irqsave(&vc->lock, flags);
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if (vc->vd_terminated) {
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vchan_vdesc_fini(vc->vd_terminated);
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vc->vd_terminated = NULL;
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}
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spin_unlock_irqrestore(&vc->lock, flags);
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}
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#endif
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