From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinod Koul Subject: Re: [PATCH 09/13] dmaengine: edma: check for echan->edesc => NULL in edma_dma_pause() Date: Wed, 15 Oct 2014 20:57:00 +0530 Message-ID: <20141015152700.GY1638@intel.com> References: <1412014009-13315-1-git-send-email-bigeasy@linutronix.de> <1412014009-13315-10-git-send-email-bigeasy@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1412014009-13315-10-git-send-email-bigeasy@linutronix.de> Sender: linux-serial-owner@vger.kernel.org To: Sebastian Andrzej Siewior Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tony@atomide.com, balbi@ti.com, gregkh@linuxfoundation.org List-Id: linux-omap@vger.kernel.org On Mon, Sep 29, 2014 at 08:06:45PM +0200, Sebastian Andrzej Siewior wrote: > I added book keeping of whether or not the 8250-dma driver has an RX > transfer pending or not so we don't BUG here if it calls > dmaengine_pause() on a channel which has not a pending transfer. Guess > what, this is not enough. > The following can be triggered with a busy RX channel and hackbench in > background: > - DMA transfer completes. The callback is delayed via > vchan_cookie_complete() into a tasklet so it das not happen asap. > - hackbench keeps the system busy so the tasklet does not run "soon". > - the UART collected enough data and generates an "timeout"-interrupt. > Since 8250-dma *thinks* the DMA-transfer is still pending it tries to > cancel it via invoking dmaengine_pause() first. This causes the segfault > because echan->edesc is NULL now that the transfer completed (however > the callback did not run yet). > > With this patch we don't BUG in the scenario described. Applied thanks -- ~Vinod > > Cc: vinod.koul@intel.com > Signed-off-by: Sebastian Andrzej Siewior > --- > drivers/dma/edma.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c > index 7b65633f495e..123f578d6dd3 100644 > --- a/drivers/dma/edma.c > +++ b/drivers/dma/edma.c > @@ -288,7 +288,7 @@ static int edma_slave_config(struct edma_chan *echan, > static int edma_dma_pause(struct edma_chan *echan) > { > /* Pause/Resume only allowed with cyclic mode */ > - if (!echan->edesc->cyclic) > + if (!echan->edesc || !echan->edesc->cyclic) > return -EINVAL; > > edma_pause(echan->ch_num); > -- > 2.1.0 > --