On Monday 12 August 2013 09:59 AM, Joel Fernandes wrote: > 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. Okay, I wont queue for -rc then. If Vinod wants to take this along with rest of the series, you can add my: Acked-by: Sekhar Nori <nsekhar@xxxxxx> Thanks, Sekhar -- 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
