Currently, it is effectively impossible to offline CPUs. Since, most
CPUs will have vmbus channels attached to them. So, as made mention of
in commit d570aec0f2154 ("Drivers: hv: vmbus: Synchronize
init_vp_index() vs. CPU hotplug"), rebind channels associated with CPUs
that a user is trying to offline to a new "randomly" selected CPU.Cc: Boqun Feng <[email protected]> Cc: Wei Liu <[email protected]> Signed-off-by: Hamza Mahfooz <[email protected]> --- v2: remove cpus_read_{un,}lock() from hv_pick_new_cpu() and add lockdep_assert_cpus_held(). --- drivers/hv/hv.c | 56 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 41 insertions(+), 15 deletions(-) diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c index 36d9ba097ff5..9fef71403c86 100644 --- a/drivers/hv/hv.c +++ b/drivers/hv/hv.c @@ -433,13 +433,39 @@ static bool hv_synic_event_pending(void) return pending; } +static int hv_pick_new_cpu(struct vmbus_channel *channel, + unsigned int current_cpu) +{ + int ret = 0; + int cpu; + + lockdep_assert_cpus_held(); + lockdep_assert_held(&vmbus_connection.channel_mutex); + + /* + * We can't assume that the relevant interrupts will be sent before + * the cpu is offlined on older versions of hyperv. + */ + if (vmbus_proto_version < VERSION_WIN10_V5_3) + return -EBUSY; + + cpu = cpumask_next(get_random_u32_below(nr_cpu_ids), cpu_online_mask); + + if (cpu >= nr_cpu_ids || cpu == current_cpu) + cpu = VMBUS_CONNECT_CPU; + + ret = vmbus_channel_set_cpu(channel, cpu); + + return ret; +} + /* * hv_synic_cleanup - Cleanup routine for hv_synic_init(). */ int hv_synic_cleanup(unsigned int cpu) { struct vmbus_channel *channel, *sc; - bool channel_found = false; + int ret = 0; if (vmbus_connection.conn_state != CONNECTED) goto always_cleanup; @@ -456,31 +482,31 @@ int hv_synic_cleanup(unsigned int cpu) /* * Search for channels which are bound to the CPU we're about to - * cleanup. In case we find one and vmbus is still connected, we - * fail; this will effectively prevent CPU offlining. - * - * TODO: Re-bind the channels to different CPUs. + * cleanup. */ mutex_lock(&vmbus_connection.channel_mutex); list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) { if (channel->target_cpu == cpu) { - channel_found = true; - break; + ret = hv_pick_new_cpu(channel, cpu); + + if (ret) { + mutex_unlock(&vmbus_connection.channel_mutex); + return ret; + } } list_for_each_entry(sc, &channel->sc_list, sc_list) { if (sc->target_cpu == cpu) { - channel_found = true; - break; + ret = hv_pick_new_cpu(channel, cpu); + + if (ret) { + mutex_unlock(&vmbus_connection.channel_mutex); + return ret; + } } } - if (channel_found) - break; } mutex_unlock(&vmbus_connection.channel_mutex); - if (channel_found) - return -EBUSY; - /* * channel_found == false means that any channels that were previously * assigned to the CPU have been reassigned elsewhere with a call of @@ -497,5 +523,5 @@ int hv_synic_cleanup(unsigned int cpu) hv_synic_disable_regs(cpu); - return 0; + return ret; } -- 2.47.1
