On Sun, Aug 11, 2013 at 11:25 PM, Sekhar Nori <nsekhar@xxxxxx> 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@xxxxxx> >> >> 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-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
