From: Waiman Long <[email protected]> Sent: Thursday, August 27, 2026 12:38 PM
>
> There is a retry loop in init_vp_index() where the CPUs from a certain
> node are stripped out if they have already been in the allocated cpumask
> or not in HK_TYPE_MANAGED_IRQ housekeeping cpumask. If there is no
> CPU left, the allocated cpumask is ignored and the process is retried
> again. However, if the HK_TYPE_MANAGED_IRQ housekeeping cpumask turns
> out not to contain any CPU in that particular node, that will become an
> infinite retry loop. This particular problem was reported by sashiko
> [1]. This should rarely happen, but we still need to guard against this.
>
> Fix this infinite loop problem by also skipping NUMA node that has no
> housekeeping CPU in the inner while loop of init_vp_index(). As the outer
> for loop will only be reached if the housekeeping cpumask isn't empty,
> a NUMA node with housekeeping CPUs will eventually be found.
>
> Link:
> https://sashiko.dev/#/message/20260422030903.E1BFCC2BCB0%40smtp.kernel.org [1]
> Fixes: 6640b5df1a38 ("Drivers: hv: vmbus: Don't assign VMbus channel
> interrupts to isolated CPUs")
> Signed-off-by: Waiman Long <[email protected]>
> ---
> drivers/hv/channel_mgmt.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 89d214dda360..ed121d74d73f 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -752,6 +752,7 @@ static void init_vp_index(struct vmbus_channel *channel)
> u32 i, ncpu = num_online_cpus();
> cpumask_var_t available_mask;
> struct cpumask *allocated_mask;
> + const struct cpumask *node_mask;
> const struct cpumask *hk_mask =
> housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);
> u32 target_cpu;
> int numa_node;
> @@ -780,14 +781,16 @@ static void init_vp_index(struct vmbus_channel *channel)
> next_numa_node_id = 0;
> continue;
> }
> - if (cpumask_empty(cpumask_of_node(numa_node)))
> + node_mask = cpumask_of_node(numa_node);
> + if (cpumask_empty(node_mask) ||
> + !cpumask_intersects(node_mask, hk_mask))
The cpumask_empty() test looks to be redundant. The
cpumask_intersects() test will catch the case where
node_mask is empty.
Otherwise, I think this looks good as a solution to the core
problem.
Michael
> continue;
> break;
> }
> allocated_mask = &hv_context.hv_numa_map[numa_node];
>
> retry:
> - cpumask_xor(available_mask, allocated_mask,
> cpumask_of_node(numa_node));
> + cpumask_xor(available_mask, allocated_mask, node_mask);
> cpumask_and(available_mask, available_mask, hk_mask);
>
> if (cpumask_empty(available_mask)) {
> --
> 2.55.0
>
