dmaengine: virt-dma: Support for race free transfer termination (1c7f072d) · Commits · 戴 / test

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>

drivers/dma/virt-dma.h

+30 −0

Original line number	Diff line number	Diff line
		@@ -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

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