Drivers: hv: vmbus: fix the race when querying & updating the percpu list

There is a rare race when we remove an entry from the global list
hv_context.percpu_list[cpu] in hv_process_channel_removal() ->
percpu_channel_deq() -> list_del(): at this time, if vmbus_on_event() ->
process_chn_event() -> pcpu_relid2channel() is trying to query the list,
we can get the kernel fault.

Similarly, we also have the issue in the code path: vmbus_process_offer() ->
percpu_channel_enq().

We can resolve the issue by disabling the tasklet when updating the list.

The patch also moves vmbus_release_relid() to a later place where
the channel has been removed from the per-cpu and the global lists.

Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 9a88c63..e47d37d 100644 (file)
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -505,7 +505,6 @@ static void reset_channel_cb(void *arg)
 static int vmbus_close_internal(struct vmbus_channel *channel)
 {
        struct vmbus_channel_close_channel *msg;
-       struct tasklet_struct *tasklet;
        int ret;
 
        /*
@@ -517,8 +516,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
         * To resolve the race, we can serialize them by disabling the
         * tasklet when the latter is running here.
         */
-       tasklet = hv_context.event_dpc[channel->target_cpu];
-       tasklet_disable(tasklet);
+       hv_event_tasklet_disable(channel);
 
        /*
         * In case a device driver's probe() fails (e.g.,
@@ -584,7 +582,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
                get_order(channel->ringbuffer_pagecount * PAGE_SIZE));
 
 out:
-       tasklet_enable(tasklet);
+       hv_event_tasklet_enable(channel);
 
        return ret;
 }

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index b6c1211..8818b92 100644 (file)
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -21,6 +21,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
+#include <linux/interrupt.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/mm.h>
@@ -303,16 +304,32 @@ static void vmbus_release_relid(u32 relid)
        vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released));
 }
 
+void hv_event_tasklet_disable(struct vmbus_channel *channel)
+{
+       struct tasklet_struct *tasklet;
+       tasklet = hv_context.event_dpc[channel->target_cpu];
+       tasklet_disable(tasklet);
+}
+
+void hv_event_tasklet_enable(struct vmbus_channel *channel)
+{
+       struct tasklet_struct *tasklet;
+       tasklet = hv_context.event_dpc[channel->target_cpu];
+       tasklet_enable(tasklet);
+
+       /* In case there is any pending event */
+       tasklet_schedule(tasklet);
+}
+
 void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)
 {
        unsigned long flags;
        struct vmbus_channel *primary_channel;
 
-       vmbus_release_relid(relid);
-
        BUG_ON(!channel->rescind);
        BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
 
+       hv_event_tasklet_disable(channel);
        if (channel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(channel->target_cpu,
@@ -321,6 +338,7 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)
                percpu_channel_deq(channel);
                put_cpu();
        }
+       hv_event_tasklet_enable(channel);
 
        if (channel->primary_channel == NULL) {
                list_del(&channel->listentry);
@@ -341,6 +359,8 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)
        cpumask_clear_cpu(channel->target_cpu,
                          &primary_channel->alloced_cpus_in_node);
 
+       vmbus_release_relid(relid);
+
        free_channel(channel);
 }
 
@@ -409,6 +429,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 
        init_vp_index(newchannel, dev_type);
 
+       hv_event_tasklet_disable(newchannel);
        if (newchannel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(newchannel->target_cpu,
@@ -418,6 +439,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
                percpu_channel_enq(newchannel);
                put_cpu();
        }
+       hv_event_tasklet_enable(newchannel);
 
        /*
         * This state is used to indicate a successful open
@@ -463,12 +485,11 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
        return;
 
 err_deq_chan:
-       vmbus_release_relid(newchannel->offermsg.child_relid);
-
        mutex_lock(&vmbus_connection.channel_mutex);
        list_del(&newchannel->listentry);
        mutex_unlock(&vmbus_connection.channel_mutex);
 
+       hv_event_tasklet_disable(newchannel);
        if (newchannel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(newchannel->target_cpu,
@@ -477,6 +498,9 @@ err_deq_chan:
                percpu_channel_deq(newchannel);
                put_cpu();
        }
+       hv_event_tasklet_enable(newchannel);
+
+       vmbus_release_relid(newchannel->offermsg.child_relid);
 
 err_free_chan:
        free_channel(newchannel);

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b10954a..50f493e 100644 (file)
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1357,6 +1357,9 @@ extern bool vmbus_prep_negotiate_resp(struct icmsg_hdr *,
                                        struct icmsg_negotiate *, u8 *, int,
                                        int);
 
+void hv_event_tasklet_disable(struct vmbus_channel *channel);
+void hv_event_tasklet_enable(struct vmbus_channel *channel);
+
 void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid);
 
 /*