Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754788AbbBDJdt (ORCPT ); Wed, 4 Feb 2015 04:33:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54762 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754331AbbBDJdp (ORCPT ); Wed, 4 Feb 2015 04:33:45 -0500 From: Vitaly Kuznetsov To: Jason Wang Cc: "K. Y. Srinivasan" , devel@linuxdriverproject.org, Haiyang Zhang , linux-kernel@vger.kernel.org, Dexuan Cui Subject: Re: [PATCH 1/4] Drivers: hv: vmbus: implement get/put usage workflow for vmbus channels References: <1422982839-3948-1-git-send-email-vkuznets@redhat.com> <1422982839-3948-2-git-send-email-vkuznets@redhat.com> <1423041265.10558.6@smtp.corp.redhat.com> Date: Wed, 04 Feb 2015 10:33:37 +0100 In-Reply-To: <1423041265.10558.6@smtp.corp.redhat.com> (Jason Wang's message of "Wed, 04 Feb 2015 09:22:25 +0008") Message-ID: <87386mrpfy.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8186 Lines: 244 Jason Wang writes: > On Wed, Feb 4, 2015 at 1:00 AM, Vitaly Kuznetsov > wrote: >> free_channel() function frees the channel unconditionally so we need >> to make >> sure nobody has any link to it. This is not trivial and there are >> several >> examples of races we have: >> >> 1) In vmbus_onoffer_rescind() we check for channel existence with >> relid2channel() and then use it. This can go wrong if we're in >> the middle >> of channel removal (free_channel() was already called). >> >> 2) In process_chn_event() we check for channel existence with >> pcpu_relid2channel() and then use it. This can also go wrong. >> >> 3) vmbus_free_channels() just frees all channels, in case we're in >> the middle >> of vmbus_process_rescind_offer() crash is possible. >> >> The issue can be solved by holding vmbus_connection.channel_lock >> everywhere, >> however, it looks like a way to deadlocks and performance >> degradation. Get/put >> workflow fits here the best. >> >> Implement vmbus_get_channel()/vmbus_put_channel() pair instead of >> free_channel(). >> >> Signed-off-by: Vitaly Kuznetsov >> --- >> drivers/hv/channel_mgmt.c | 45 >> ++++++++++++++++++++++++++++++++++++++------- >> drivers/hv/connection.c | 7 +++++-- >> drivers/hv/hyperv_vmbus.h | 4 ++++ >> include/linux/hyperv.h | 13 +++++++++++++ >> 4 files changed, 60 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c >> index 36bacc7..eb9ce94 100644 >> --- a/drivers/hv/channel_mgmt.c >> +++ b/drivers/hv/channel_mgmt.c >> @@ -147,6 +147,8 @@ static struct vmbus_channel *alloc_channel(void) >> return NULL; >> channel->id = atomic_inc_return(&chan_num); >> + atomic_set(&channel->count, 1); >> + >> spin_lock_init(&channel->inbound_lock); >> spin_lock_init(&channel->lock); >> @@ -178,19 +180,47 @@ static void release_channel(struct >> work_struct *work) >> } >> /* >> - * free_channel - Release the resources used by the vmbus channel >> object >> + * vmbus_put_channel - Decrease the channel usage counter and >> release the >> + * resources when this counter reaches zero. >> */ >> -static void free_channel(struct vmbus_channel *channel) >> +void vmbus_put_channel(struct vmbus_channel *channel) >> { >> + unsigned long flags; >> /* >> * We have to release the channel's workqueue/thread in the vmbus's >> * workqueue/thread context >> * ie we can't destroy ourselves. >> */ >> - INIT_WORK(&channel->work, release_channel); >> - queue_work(vmbus_connection.work_queue, &channel->work); >> + spin_lock_irqsave(&channel->lock, flags); >> + if (atomic_dec_and_test(&channel->count)) { >> + channel->dying = true; >> + INIT_WORK(&channel->work, release_channel); >> + spin_unlock_irqrestore(&channel->lock, flags); >> + queue_work(vmbus_connection.work_queue, &channel->work); >> + } else >> + spin_unlock_irqrestore(&channel->lock, flags); >> +} >> +EXPORT_SYMBOL_GPL(vmbus_put_channel); >> + >> +/* vmbus_get_channel - Get additional reference to the channel */ >> +struct vmbus_channel *vmbus_get_channel(struct vmbus_channel >> *channel) >> +{ >> + unsigned long flags; >> + struct vmbus_channel *ret = NULL; >> + >> + if (!channel) >> + return NULL; >> + >> + spin_lock_irqsave(&channel->lock, flags); >> + if (!channel->dying) { >> + atomic_inc(&channel->count); >> + ret = channel; >> + } >> + spin_unlock_irqrestore(&channel->lock, flags); > > Looks like we can use atomic_inc_return_safe() here to avoid extra > dying. And then there's also no need for the spinlock. > > if (atomic_inc_return_safe(&channel->count) > 0) > return channel; > else > return NULL; Good idea, thanks! I'll try. >> >> + return ret; >> } >> +EXPORT_SYMBOL_GPL(vmbus_get_channel); >> static void percpu_channel_enq(void *arg) >> { >> @@ -253,7 +283,7 @@ static void vmbus_process_rescind_offer(struct >> work_struct *work) >> list_del(&channel->sc_list); >> spin_unlock_irqrestore(&primary_channel->lock, flags); >> } >> - free_channel(channel); >> + vmbus_put_channel(channel); >> } >> void vmbus_free_channels(void) >> @@ -262,7 +292,7 @@ void vmbus_free_channels(void) >> list_for_each_entry(channel, &vmbus_connection.chn_list, >> listentry) { >> vmbus_device_unregister(channel->device_obj); >> - free_channel(channel); >> + vmbus_put_channel(channel); >> } >> } >> @@ -391,7 +421,7 @@ done_init_rescind: >> spin_unlock_irqrestore(&newchannel->lock, flags); >> return; >> err_free_chan: >> - free_channel(newchannel); >> + vmbus_put_channel(newchannel); >> } >> enum { >> @@ -549,6 +579,7 @@ static void vmbus_onoffer_rescind(struct >> vmbus_channel_message_header *hdr) >> queue_work(channel->controlwq, &channel->work); >> spin_unlock_irqrestore(&channel->lock, flags); >> + vmbus_put_channel(channel); >> } >> /* >> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c >> index c4acd1c..d1ce134 100644 >> --- a/drivers/hv/connection.c >> +++ b/drivers/hv/connection.c >> @@ -247,7 +247,8 @@ void vmbus_disconnect(void) >> * Map the given relid to the corresponding channel based on the >> * per-cpu list of channels that have been affinitized to this CPU. >> * This will be used in the channel callback path as we can do this >> - * mapping in a lock-free fashion. >> + * mapping in a lock-free fashion. Takes additional reference to the >> + * channel, all users are supposed to do vmbus_put_channel(). >> */ >> static struct vmbus_channel *pcpu_relid2channel(u32 relid) >> { >> @@ -263,7 +264,7 @@ static struct vmbus_channel >> *pcpu_relid2channel(u32 relid) >> } >> } >> - return found_channel; >> + return vmbus_get_channel(found_channel); >> } >> /* >> @@ -297,6 +298,7 @@ struct vmbus_channel *relid2channel(u32 relid) >> } >> } >> } >> + found_channel = vmbus_get_channel(found_channel); >> spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags); >> return found_channel; >> @@ -360,6 +362,7 @@ static void process_chn_event(u32 relid) >> pr_err("no channel callback for relid - %u\n", relid); >> } >> + vmbus_put_channel(channel); >> } >> /* >> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h >> index b055e53..40d70f0 100644 >> --- a/drivers/hv/hyperv_vmbus.h >> +++ b/drivers/hv/hyperv_vmbus.h >> @@ -687,6 +687,10 @@ void vmbus_device_unregister(struct hv_device >> *device_obj); >> /* VmbusChildDeviceDestroy( */ >> /* struct hv_device *); */ >> +/* >> + * Get the channel by its relid. Takes additional reference to the >> channel so >> + * all users are supposed to do vmbus_put_channel() when they're >> done. >> + */ >> struct vmbus_channel *relid2channel(u32 relid); >> void vmbus_free_channels(void); >> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h >> index e73cfeb..c576d2d 100644 >> --- a/include/linux/hyperv.h >> +++ b/include/linux/hyperv.h >> @@ -649,6 +649,9 @@ struct vmbus_channel { >> /* Unique channel id */ >> int id; >> + /* Active reference count */ >> + atomic_t count; >> + >> struct list_head listentry; >> struct hv_device *device_obj; >> @@ -666,6 +669,7 @@ struct vmbus_channel { >> u8 monitor_bit; >> bool rescind; /* got rescind msg */ >> + bool dying; /* channel is dying */ >> u32 ringbuffer_gpadlhandle; >> @@ -907,6 +911,15 @@ extern int vmbus_recvpacket_raw(struct >> vmbus_channel *channel, >> extern void vmbus_ontimer(unsigned long data); >> +/* >> + * Decrease reference count for the channel. Frees the channel when >> its usage >> + * count reaches zero. >> + */ >> +extern void vmbus_put_channel(struct vmbus_channel *channel); >> + >> +/* Get additional reference to the channel */ >> +extern struct vmbus_channel *vmbus_get_channel(struct vmbus_channel >> *channel); >> + >> /* Base driver object */ >> struct hv_driver { >> const char *name; >> -- >> 1.9.3 >> -- Vitaly -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/