Re: [PATCH v4 21/26] iommu/arm-smmu-v3: Ratelimit event dump

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Hi Aaro,

On Fri, May 28, 2021 at 11:09:58AM +0300, Aaro Koskinen wrote:
> Hi,
> 
> On Mon, Feb 24, 2020 at 07:23:56PM +0100, Jean-Philippe Brucker wrote:
> > When a device or driver misbehaves, it is possible to receive events
> > much faster than we can print them out. Ratelimit the printing of
> > events.
> > 
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>
> 
> > During the SVA tests when the device driver didn't properly stop DMA
> > before unbinding, the event queue thread would almost lock-up the server
> > with a flood of event 0xa. This patch helped recover from the error.
> 
> I was just debugging a similar case, and this patch was required to
> prevent system from locking up.
> 
> Could you please resend this patch independently from the other patches
> in the series, as it seems it's a worthwhile fix and still relevent for
> current kernels. Thanks,

Ok, I'll resend it

Thanks,
Jean

> 
> A.
> 
> > ---
> >  drivers/iommu/arm-smmu-v3.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> > index 28f8583cd47b..6a5987cce03f 100644
> > --- a/drivers/iommu/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm-smmu-v3.c
> > @@ -2243,17 +2243,20 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
> >  	struct arm_smmu_device *smmu = dev;
> >  	struct arm_smmu_queue *q = &smmu->evtq.q;
> >  	struct arm_smmu_ll_queue *llq = &q->llq;
> > +	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
> > +				      DEFAULT_RATELIMIT_BURST);
> >  	u64 evt[EVTQ_ENT_DWORDS];
> >  
> >  	do {
> >  		while (!queue_remove_raw(q, evt)) {
> >  			u8 id = FIELD_GET(EVTQ_0_ID, evt[0]);
> >  
> > -			dev_info(smmu->dev, "event 0x%02x received:\n", id);
> > -			for (i = 0; i < ARRAY_SIZE(evt); ++i)
> > -				dev_info(smmu->dev, "\t0x%016llx\n",
> > -					 (unsigned long long)evt[i]);
> > -
> > +			if (__ratelimit(&rs)) {
> > +				dev_info(smmu->dev, "event 0x%02x received:\n", id);
> > +				for (i = 0; i < ARRAY_SIZE(evt); ++i)
> > +					dev_info(smmu->dev, "\t0x%016llx\n",
> > +						 (unsigned long long)evt[i]);
> > +			}
> >  		}
> >  
> >  		/*