Re: [PATCH] iommu/iova: Free all CPU rcache for retry when iova alloc failure

[Robin Murphy <robin.murphy@arm.com>]

On 2022-03-04 04:46, yf.wang--- via iommu wrote:
> From: Yunfei Wang <yf.wang@mediatek.com>
> 
> In alloc_iova_fast function, if an iova alloc request fail,
> it will free the iova ranges present in the percpu iova
> rcaches and free global iova rcache and then retry, but
> flushing CPU iova rcaches only for each online CPU, which
> will cause incomplete rcache cleaning, and iova rcaches of
> not online CPU cannot be flushed, because iova rcaches may
> also lead to fragmentation of iova space, so the next retry
> action may still be fail.
> 
> Based on the above, so need to flushing all iova rcaches
> for each possible CPU, use for_each_possible_cpu instead of
> for_each_online_cpu like in free_iova_rcaches function,
> so that all rcaches can be completely released to try
> replenishing IOVAs.

OK, so either there's a mystery bug where IOVAs somehow get freed on 
offline CPUs, or the hotplug notifier isn't working correctly, or you've 
contrived a situation where alloc_iova_fast() is actually racing against 
iova_cpuhp_dead(). In the latter case, the solution is "don't do that".

This change should not be necessary.

Thanks,
Robin.

> Signed-off-by: Yunfei Wang <yf.wang@mediatek.com>
> Cc: <stable@vger.kernel.org> # 5.4.*
> ---
>   drivers/iommu/iova.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index b28c9435b898..5a0637cd7bc2 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -460,7 +460,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
>   
>   		/* Try replenishing IOVAs by flushing rcache. */
>   		flush_rcache = false;
> -		for_each_online_cpu(cpu)
> +		for_each_possible_cpu(cpu)
>   			free_cpu_cached_iovas(cpu, iovad);
>   		free_global_cached_iovas(iovad);
>   		goto retry;
> 
> 
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