From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755720AbdKNOgO (ORCPT ); Tue, 14 Nov 2017 09:36:14 -0500 Received: from lelnx194.ext.ti.com ([198.47.27.80]:17820 "EHLO lelnx194.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755543AbdKNOcQ (ORCPT ); Tue, 14 Nov 2017 09:32:16 -0500 From: Peter Ujfalusi To: CC: , , , Subject: [PATCH 02/10] dmaengine: virt-dma: Support for race free transfer termination Date: Tue, 14 Nov 2017 16:32:04 +0200 Message-ID: <20171114143212.8311-3-peter.ujfalusi@ti.com> X-Mailer: git-send-email 2.15.0 In-Reply-To: <20171114143212.8311-1-peter.ujfalusi@ti.com> References: <20171114143212.8311-1-peter.ujfalusi@ti.com> MIME-Version: 1.0 Content-Type: text/plain X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- drivers/dma/virt-dma.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h index 2edb05505102..b09b75ab0751 100644 --- a/drivers/dma/virt-dma.h +++ b/drivers/dma/virt-dma.h @@ -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 -- Peter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki