Drivers: hv: vmbus: Resolve more races involving init_vp_index()

init_vp_index() uses the (per-node) hv_numa_map[] masks to record the
CPUs allocated for channel interrupts at a given time, and distribute
the performance-critical channels across the available CPUs: in part.,
the mask of "candidate" target CPUs in a given NUMA node, for a newly
offered channel, is determined by XOR-ing the node's CPU mask and the
node's hv_numa_map.  This operation/mechanism assumes that no offline
CPUs is set in the hv_numa_map mask, an assumption that does not hold
since such mask is currently not updated when a channel is removed or
assigned to a different CPU.

To address the issues described above, this adds hooks in the channel
removal path (hv_process_channel_removal()) and in target_cpu_store()
in order to clear, resp. to update, the hv_numa_map[] masks as needed.
This also adds a (missed) update of the masks in init_vp_index() (cf.,
e.g., the memory-allocation failure path in this function).

Like in the case of init_vp_index(), such hooks require to determine
if the given channel is performance critical.  init_vp_index() does
this by parsing the channel's offer, it can not rely on the device
data structure (device_obj) to retrieve such information because the
device data structure has not been allocated/linked with the channel
by the time that init_vp_index() executes.  A similar situation may
hold in hv_is_alloced_cpu() (defined below); the adopted approach is
to "cache" the device type of the channel, as computed by parsing the
channel's offer, in the channel structure itself.

Fixes: 7527810573436f ("Drivers: hv: vmbus: Introduce the CHANNELMSG_MODIFYCHANNEL message type")
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20200522171901.204127-3-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index c2a4a7c0b99a..47747755d2e1 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1687,8 +1687,8 @@ static ssize_t target_cpu_show(struct vmbus_channel *channel, char *buf)
 static ssize_t target_cpu_store(struct vmbus_channel *channel,
 				const char *buf, size_t count)
 {
+	u32 target_cpu, origin_cpu;
 	ssize_t ret = count;
-	u32 target_cpu;
 
 	if (vmbus_proto_version < VERSION_WIN10_V4_1)
 		return -EIO;
@@ -1741,7 +1741,8 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 		goto cpu_store_unlock;
 	}
 
-	if (channel->target_cpu == target_cpu)
+	origin_cpu = channel->target_cpu;
+	if (target_cpu == origin_cpu)
 		goto cpu_store_unlock;
 
 	if (vmbus_send_modifychannel(channel->offermsg.child_relid,
@@ -1763,14 +1764,20 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 	 * in on a CPU that is different from the channel target_cpu value.
 	 */
 
-	if (channel->change_target_cpu_callback)
-		(*channel->change_target_cpu_callback)(channel,
-				channel->target_cpu, target_cpu);
-
 	channel->target_cpu = target_cpu;
 	channel->target_vp = hv_cpu_number_to_vp_number(target_cpu);
 	channel->numa_node = cpu_to_node(target_cpu);
 
+	/* See init_vp_index(). */
+	if (hv_is_perf_channel(channel))
+		hv_update_alloced_cpus(origin_cpu, target_cpu);
+
+	/* Currently set only for storvsc channels. */
+	if (channel->change_target_cpu_callback) {
+		(*channel->change_target_cpu_callback)(channel,
+				origin_cpu, target_cpu);
+	}
+
 cpu_store_unlock:
 	mutex_unlock(&vmbus_connection.channel_mutex);
 	cpus_read_unlock();