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Date: Sun, 11 Aug 2013 23:29:33 -0500 From: Joel Fernandes <agnel.joel@...il.com> To: Sekhar Nori <nsekhar@...com> Cc: Joel Fernandes <joelf@...com>, Mark Brown <broonie@...aro.org>, Tony Lindgren <tony@...mide.com>, Grant Likely <grant.likely@...retlab.ca>, Sricharan R <r.sricharan@...com>, Russell King <linux@....linux.org.uk>, Vinod Koul <vinod.koul@...el.com>, Lokesh Vutla <lokeshvutla@...com>, Chris Ball <cjb@...top.org>, Arnd Bergmann <arnd@...db.de>, Rajendra Nayak <rnayak@...com>, Rob Herring <rob.herring@...xeda.com>, Jason Kridner <jkridner@...gleboard.org>, Linux OMAP List <linux-omap@...r.kernel.org>, Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>, Linux DaVinci Kernel List <davinci-linux-open-source@...ux.davincidsp.com>, Balaji TK <balajitk@...com>, Linux MMC List <linux-mmc@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Santosh Shilimkar <santosh.shilimkar@...com>, Dan Williams <djbw@...com>, Olof Johansson <olof@...om.net>, Benoit Cousson <benoit.cousson@...aro.org> Subject: Re: [PATCH v3 02/12] ARM: edma: Don't clear EMR of channel in edma_stop On Sun, Aug 11, 2013 at 11:25 PM, Sekhar Nori <nsekhar@...com> wrote: > On 8/8/2013 5:19 PM, Sekhar Nori wrote: >> On Monday 05 August 2013 09:44 PM, Joel Fernandes wrote: >>> We certainly don't want error conditions to be cleared any other >>> place but the EDMA error handler, as this will make us 'forget' >>> about missed events we might need to know errors have occurred. >>> >>> This fixes a race condition where the EMR was being cleared >>> by the transfer completion interrupt handler. >>> >>> Basically, what was happening was: >>> >>> Missed event >>> | >>> | >>> V >>> SG1-SG2-SG3-Null >>> \ >>> \__TC Interrupt (Almost same time as ARM is executing >>> TC interrupt handler, an event got missed and also forgotten >>> by clearing the EMR). >>> >>> This causes the following problems: >>> >>> 1. >>> If error interrupt is also pending and TC interrupt clears the EMR >>> by calling edma_stop as has been observed in the edma_callback function, >>> the ARM will execute the error interrupt even though the EMR is clear. >>> As a result, the dma_ccerr_handler returns IRQ_NONE. If this happens >>> enough number of times, IRQ subsystem disables the interrupt thinking >>> its spurious which makes error handler never execute again. >>> >>> 2. >>> Also even if error handler doesn't return IRQ_NONE, the removing of EMR >>> removes the knowledge about which channel had a missed event, and thus >>> a manual trigger on such channels cannot be performed. >>> >>> The EMR is ultimately being cleared by the Error interrupt handler >>> once it is handled so we remove code that does it in edma_stop and >>> allow it to happen there. >>> >>> Signed-off-by: Joel Fernandes <joelf@...com> >> >> Queuing this for v3.11 fixes. While committing, I changed the headline >> to remove capitalization and made it more readable by removing register >> level details. The new headline is: >> >> ARM: edma: don't clear missed events in edma_stop() > > Forgot to ask, should this be tagged for stable? IOW, how serious is > this race in current kernel (without the entire series applied)? I have > never observed it myself - so please provide details how easy/difficult > it is to hit this condition. The race was uncovered by recent EDMA patch series, So this patch can go in for next kernel release as such, I am not aware of any other DMA user that maybe uncovering the race condition. Thanks, -Joel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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