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Subject[PATCH v3] Drivers: hv: vmbus: fix the race when querying & updating the percpu list
Date
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>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

v2: added tasklet_schedule() after tasklet_enable(). Thanks, Vitaly!

v3: I shouldn't have moved percpu_channel_deq()
from hv_process_channel_removal() to vmbus_close_internal(): the
channel couldn't be removed from the per-cpu list, if the channel state
was not CHANNEL_OPENED_STATE. v3 fixed this.

v3 also added 2 wrapper functions for the disable/enable stuff.
v3 also moved vmbus_release_relid() to a later safe place.

You can also get v3 by
https://github.com/dcui/linux/commit/2f314fb9352020f70b094bf31539afd3a18a5545

drivers/hv/channel.c | 6 ++----
drivers/hv/channel_mgmt.c | 32 ++++++++++++++++++++++++++++----
include/linux/hyperv.h | 3 +++
3 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 56dd261..ef8e9b5 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -512,7 +512,6 @@ 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;

/*
@@ -524,8 +523,7 @@ 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.,
@@ -591,7 +589,7 @@ 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 38b682ba..3bcf141 100644
--- 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(channel);
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(channel);

/*
* 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(channel);
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(channel);
+
+ 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 7be7237..8070cda 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1328,6 +1328,9 @@ 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);

/*
--
2.1.0
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