Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756192AbbBCRBY (ORCPT ); Tue, 3 Feb 2015 12:01:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35794 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965602AbbBCRBW (ORCPT ); Tue, 3 Feb 2015 12:01:22 -0500 From: Vitaly Kuznetsov To: "K. Y. Srinivasan" , devel@linuxdriverproject.org Cc: Haiyang Zhang , linux-kernel@vger.kernel.org, Dexuan Cui , Jason Wang Subject: [PATCH 1/4] Drivers: hv: vmbus: implement get/put usage workflow for vmbus channels Date: Tue, 3 Feb 2015 18:00:36 +0100 Message-Id: <1422982839-3948-2-git-send-email-vkuznets@redhat.com> In-Reply-To: <1422982839-3948-1-git-send-email-vkuznets@redhat.com> References: <1422982839-3948-1-git-send-email-vkuznets@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7164 Lines: 229 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); + 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 -- 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/