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Date: Fri, 17 Jul 2015 18:09:44 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: KY Srinivasan <kys@...rosoft.com>
Cc: "davem\@davemloft.net" <davem@...emloft.net>,
"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
"devel\@linuxdriverproject.org" <devel@...uxdriverproject.org>,
"olaf\@aepfle.de" <olaf@...fle.de>,
"apw\@canonical.com" <apw@...onical.com>,
"jasowang\@redhat.com" <jasowang@...hat.com>,
Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be processed during probe
KY Srinivasan <kys@...rosoft.com> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
>> Sent: Friday, July 17, 2015 7:13 AM
>> To: KY Srinivasan
>> Cc: davem@...emloft.net; netdev@...r.kernel.org; linux-
>> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
>> apw@...onical.com; jasowang@...hat.com; Dexuan Cui
>> Subject: Re: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be
>> processed during probe
>>
>> "K. Y. Srinivasan" <kys@...rosoft.com> writes:
>>
>> > The current code returns from probe without waiting for the proper
>> handling
>> > of subchannels that may be requested. If the netvsc driver were to be
>> rapidly
>> > loaded/unloaded, we can trigger a panic as the unload will be tearing
>> > down state that may not have been fully setup yet. We fix this issue by
>> making
>> > sure that we return from the probe call only after ensuring that the
>> > sub-channel offers in flight are properly handled.
>> >
>> > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
>> > Reviewed-and-tested-by: Haiyang Zhang <haiyangz@...rosoft.com
>> > ---
>> > drivers/net/hyperv/hyperv_net.h | 2 ++
>> > drivers/net/hyperv/rndis_filter.c | 25 +++++++++++++++++++++++++
>> > 2 files changed, 27 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/drivers/net/hyperv/hyperv_net.h
>> b/drivers/net/hyperv/hyperv_net.h
>> > index 26cd14c..925b75d 100644
>> > --- a/drivers/net/hyperv/hyperv_net.h
>> > +++ b/drivers/net/hyperv/hyperv_net.h
>> > @@ -671,6 +671,8 @@ struct netvsc_device {
>> > u32 send_table[VRSS_SEND_TAB_SIZE];
>> > u32 max_chn;
>> > u32 num_chn;
>> > + spinlock_t sc_lock; /* Protects num_sc_offered variable */
>> > + u32 num_sc_offered;
>> > atomic_t queue_sends[NR_CPUS];
>> >
>> > /* Holds rndis device info */
>> > diff --git a/drivers/net/hyperv/rndis_filter.c
>> b/drivers/net/hyperv/rndis_filter.c
>> > index 2e40417..2e09f3f 100644
>> > --- a/drivers/net/hyperv/rndis_filter.c
>> > +++ b/drivers/net/hyperv/rndis_filter.c
>> > @@ -984,9 +984,16 @@ static void netvsc_sc_open(struct vmbus_channel
>> *new_sc)
>> > struct netvsc_device *nvscdev;
>> > u16 chn_index = new_sc->offermsg.offer.sub_channel_index;
>> > int ret;
>> > + unsigned long flags;
>> >
>> > nvscdev = hv_get_drvdata(new_sc->primary_channel->device_obj);
>> >
>> > + spin_lock_irqsave(&nvscdev->sc_lock, flags);
>> > + nvscdev->num_sc_offered--;
>> > + spin_unlock_irqrestore(&nvscdev->sc_lock, flags);
>> > + if (nvscdev->num_sc_offered == 0)
>> > + complete(&nvscdev->channel_init_wait);
>> > +
>> > if (chn_index >= nvscdev->num_chn)
>> > return;
>> >
>> > @@ -1015,8 +1022,10 @@ int rndis_filter_device_add(struct hv_device
>> *dev,
>> > u32 rsscap_size = sizeof(struct ndis_recv_scale_cap);
>> > u32 mtu, size;
>> > u32 num_rss_qs;
>> > + u32 sc_delta;
>> > const struct cpumask *node_cpu_mask;
>> > u32 num_possible_rss_qs;
>> > + unsigned long flags;
>> >
>> > rndis_device = get_rndis_device();
>> > if (!rndis_device)
>> > @@ -1039,6 +1048,8 @@ int rndis_filter_device_add(struct hv_device
>> *dev,
>> > net_device->max_chn = 1;
>> > net_device->num_chn = 1;
>> >
>> > + spin_lock_init(&net_device->sc_lock);
>> > +
>> > net_device->extension = rndis_device;
>> > rndis_device->net_dev = net_device;
>> >
>> > @@ -1116,6 +1127,9 @@ int rndis_filter_device_add(struct hv_device
>> *dev,
>> > num_possible_rss_qs = cpumask_weight(node_cpu_mask);
>> > net_device->num_chn = min(num_possible_rss_qs, num_rss_qs);
>> >
>> > + num_rss_qs = net_device->num_chn - 1;
>> > + net_device->num_sc_offered = num_rss_qs;
>> > +
>> > if (net_device->num_chn == 1)
>> > goto out;
>> >
>> > @@ -1157,11 +1171,22 @@ int rndis_filter_device_add(struct hv_device
>> *dev,
>> >
>> > ret = rndis_filter_set_rss_param(rndis_device, net_device-
>> >num_chn);
>> >
>> > + /*
>> > + * Wait for the host to send us the sub-channel offers.
>> > + */
>> > + spin_lock_irqsave(&net_device->sc_lock, flags);
>> > + sc_delta = net_device->num_chn - 1 - num_rss_qs;
>> > + net_device->num_sc_offered -= sc_delta;
>> > + spin_unlock_irqrestore(&net_device->sc_lock, flags);
>> > +
>> > + if (net_device->num_sc_offered != 0)
>> > + wait_for_completion(&net_device->channel_init_wait);
>>
>> I'd suggest we add an essentian timeout (big, let's say 30 sec.)
>> here. In case something goes wrong we don't really want to hang the
>> whole kernel for forever. Such bugs are hard to debug as if a 'kernel
>> hangs' is reported we can't be sure which wait caused it. We can even
>> have something like:
>>
>> t = wait_for_completion_timeout(&net_device->channel_init_wait, 30*HZ);
>> BUG_ON(t == 0);
>>
>> This is much better as we'll be sure what went wrong. (I know other
>> pieces of hyper-v code use wait_for_completion() without a timeout, this
>> is rather a general suggestion for all of them).
>
> There is some history here. Initially, I had timeout for calls where we could reasonably
> rollback state if we timed out. Some calls were subsequently changed to unconditional
> wait because under some load conditions, these timeouts would trigger (granted I did not
> have 30 second timeout; it was a 5 second timeout).
>
> Greg was opposed to calls to BUG_ON() in general for drivers.
Even WARN() in my opinion should do the job: we'll at least have
something in the log.
> Consequently, I have chosen to
> wait unconditionally in cases where there is no sensible rollback if we were to timeout (rather
> thank bug checking).
(irrelevant to this patch but) in that case I'd suggest we have
something like:
while (1) {
t = wait_for_completion_timeout(&..., 10*HZ);
if (t)
break;
WARN(1, "Timeout while waiting for hypervisor to reply! Keep waiting...");
}
The sole purpose of that is to have something in dmesg.
>
> In this specific case though, we can have a timeout and we don't need to bug check if we timeout.
>
> I will make this change and resubmit.
Thanks!
>
> Thanks,
>
> K. Y
>>
>> > out:
>> > if (ret) {
>> > net_device->max_chn = 1;
>> > net_device->num_chn = 1;
>> > }
>> > +
>> > return 0; /* return 0 because primary channel can be used alone */
>> >
>> > err_dev_remv:
>>
>> --
>> Vitaly
--
Vitaly
--
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