KY Srinivasan <kys@xxxxxxxxxxxxx> writes: >> -----Original Message----- >> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] >> Sent: Friday, July 17, 2015 7:13 AM >> To: KY Srinivasan >> Cc: davem@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; >> apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; Dexuan Cui >> Subject: Re: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be >> processed during probe >> >> "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> >> > Reviewed-and-tested-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx >> > --- >> > 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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
