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Subject[PATCH 1/1] Drivers: hv: vmbus: Fix rescind handling issues
Date
From: K. Y. Srinivasan <kys@microsoft.com>

This patch handles the following issues that were observed when we are
handling racing channel offer message and rescind message for the same
offer:

1. Since the host does not respond to messages on a rescinded channel,
in the current code, we could be indefinitely blocked on the vmbus_open() call.

2. When a rescinded channel is being closed, if there is a pending interrupt on the
channel, we could end up freeing the channel that the interrupt handler would run on.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
---
drivers/hv/channel.c | 14 ++++++++++++++
drivers/hv/channel_mgmt.c | 29 ++++++++++++++++++++++++++---
drivers/hv/vmbus_drv.c | 3 +++
include/linux/hyperv.h | 2 ++
4 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index e9bf0bb..966a823 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -177,6 +177,11 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
&vmbus_connection.chn_msg_list);
spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

+ if (newchannel->rescind) {
+ err = -ENODEV;
+ goto error_free_gpadl;
+ }
+
ret = vmbus_post_msg(open_msg,
sizeof(struct vmbus_channel_open_channel), true);

@@ -421,6 +426,11 @@ int vmbus_establish_gpadl(struct vmbus_channel *channel, void *kbuffer,

spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

+ if (channel->rescind) {
+ ret = -ENODEV;
+ goto cleanup;
+ }
+
ret = vmbus_post_msg(gpadlmsg, msginfo->msgsize -
sizeof(*msginfo), true);
if (ret != 0)
@@ -494,6 +504,10 @@ int vmbus_teardown_gpadl(struct vmbus_channel *channel, u32 gpadl_handle)
list_add_tail(&info->msglistentry,
&vmbus_connection.chn_msg_list);
spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+ if (channel->rescind)
+ goto post_msg_err;
+
ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_gpadl_teardown),
true);

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 4bbb8de..968af17 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -451,6 +451,12 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
/* Make sure this is a new offer */
mutex_lock(&vmbus_connection.channel_mutex);

+ /*
+ * Now that we have acquired the channel_mutex,
+ * we can release the potentially racing rescind thread.
+ */
+ atomic_dec(&vmbus_connection.offer_in_progress);
+
list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
if (!uuid_le_cmp(channel->offermsg.offer.if_type,
newchannel->offermsg.offer.if_type) &&
@@ -481,7 +487,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
channel->num_sc++;
spin_unlock_irqrestore(&channel->lock, flags);
} else {
- atomic_dec(&vmbus_connection.offer_in_progress);
goto err_free_chan;
}
}
@@ -510,7 +515,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
if (!fnew) {
if (channel->sc_creation_callback != NULL)
channel->sc_creation_callback(newchannel);
- atomic_dec(&vmbus_connection.offer_in_progress);
return;
}

@@ -541,7 +545,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
goto err_deq_chan;
}

- atomic_dec(&vmbus_connection.offer_in_progress);
+ newchannel->probe_done = true;
return;

err_deq_chan:
@@ -882,8 +886,27 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
channel->rescind = true;
spin_unlock_irqrestore(&channel->lock, flags);

+ /*
+ * Now that we have posted the rescind state, perform
+ * rescind related cleanup.
+ */
vmbus_rescind_cleanup(channel);

+ /*
+ * Now wait for offer handling to complete.
+ */
+ while (READ_ONCE(channel->probe_done) == false) {
+ /*
+ * We wait here until any channel offer is currently
+ * being processed.
+ */
+ msleep(1);
+ }
+
+ /*
+ * At this point, the rescind handling can proceed safely.
+ */
+
if (channel->device_obj) {
if (channel->chn_rescind_callback) {
channel->chn_rescind_callback(channel);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index ed84e96..43160a2 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -940,6 +940,9 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
if (channel->offermsg.child_relid != relid)
continue;

+ if (channel->rescind)
+ continue;
+
switch (channel->callback_mode) {
case HV_CALL_ISR:
vmbus_channel_isr(channel);
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 27db4e6..07650d0 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -879,6 +879,8 @@ struct vmbus_channel {
*/
enum hv_numa_policy affinity_policy;

+ bool probe_done;
+
};

static inline bool is_hvsock_channel(const struct vmbus_channel *c)
--
1.7.1
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