On 8/27/26 5:10 PM, Michael Kelley wrote:
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
Yes, I am aware that cpumask_empty() test is redundant and can be
skipped. I keep it just to make it easier to read. I can certainly drop
the cpumask_empty() statement.
Cheers,
Longman
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
