From: Waiman Long <[email protected]> Sent: Friday, August 28, 2026 6:22 PM > > 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. >
The flip side is people like me try to figure out "why is this here?", thinking there must be a reason. :-) I'd say drop the code and add a comment like "Also catches an empty node_mask". Michael
