Date:   Fri, 9 Apr 2021 15:38:14 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: RE: [RFC PATCH hyperv-next] scsi: storvsc: Use blk_mq_unique_tag() to
 generate requestIDs

From: Andrea Parri (Microsoft) <parri.andrea@...il.com> Sent: Thursday, April 8, 2021 9:13 AM
> 
> Use blk_mq_unique_tag() to generate requestIDs for StorVSC, avoiding
> all issues with allocating enough entries in the VMbus requestor.

This looks good to me!  I'm glad to see that the idea worked without
too much complexity.

See a few comments inline below.

> 
> Suggested-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
> ---
>  drivers/hv/channel.c              | 14 +++---
>  drivers/hv/ring_buffer.c          | 12 ++---
>  drivers/net/hyperv/netvsc.c       |  8 ++--
>  drivers/net/hyperv/rndis_filter.c |  2 +
>  drivers/scsi/storvsc_drv.c        | 73 ++++++++++++++++++++++++++-----
>  include/linux/hyperv.h            | 13 +++++-
>  6 files changed, 92 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index db30be8f9ccea..f78e02ace51e8 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -1121,15 +1121,14 @@ EXPORT_SYMBOL_GPL(vmbus_recvpacket_raw);
>   * vmbus_next_request_id - Returns a new request id. It is also
>   * the index at which the guest memory address is stored.
>   * Uses a spin lock to avoid race conditions.
> - * @rqstor: Pointer to the requestor struct
> + * @channel: Pointer to the VMbus channel struct
>   * @rqst_add: Guest memory address to be stored in the array
>   */
> -u64 vmbus_next_request_id(struct vmbus_requestor *rqstor, u64 rqst_addr)
> +u64 vmbus_next_request_id(struct vmbus_channel *channel, u64 rqst_addr)
>  {
> +	struct vmbus_requestor *rqstor = &channel->requestor;
>  	unsigned long flags;
>  	u64 current_id;
> -	const struct vmbus_channel *channel =
> -		container_of(rqstor, const struct vmbus_channel, requestor);
> 
>  	/* Check rqstor has been initialized */
>  	if (!channel->rqstor_size)
> @@ -1163,16 +1162,15 @@ EXPORT_SYMBOL_GPL(vmbus_next_request_id);
>  /*
>   * vmbus_request_addr - Returns the memory address stored at @trans_id
>   * in @rqstor. Uses a spin lock to avoid race conditions.
> - * @rqstor: Pointer to the requestor struct
> + * @channel: Pointer to the VMbus channel struct
>   * @trans_id: Request id sent back from Hyper-V. Becomes the requestor's
>   * next request id.
>   */
> -u64 vmbus_request_addr(struct vmbus_requestor *rqstor, u64 trans_id)
> +u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id)
>  {
> +	struct vmbus_requestor *rqstor = &channel->requestor;
>  	unsigned long flags;
>  	u64 req_addr;
> -	const struct vmbus_channel *channel =
> -		container_of(rqstor, const struct vmbus_channel, requestor);
> 
>  	/* Check rqstor has been initialized */
>  	if (!channel->rqstor_size)
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index ecd82ebfd5bc4..46d8e038e4ee1 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -310,10 +310,12 @@ int hv_ringbuffer_write(struct vmbus_channel *channel,
>  	 */
> 
>  	if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) {
> -		rqst_id = vmbus_next_request_id(&channel->requestor, requestid);
> -		if (rqst_id == VMBUS_RQST_ERROR) {
> -			spin_unlock_irqrestore(&outring_info->ring_lock, flags);
> -			return -EAGAIN;
> +		if (channel->next_request_id_callback != NULL) {
> +			rqst_id = channel->next_request_id_callback(channel, requestid);
> +			if (rqst_id == VMBUS_RQST_ERROR) {
> +				spin_unlock_irqrestore(&outring_info->ring_lock, flags);
> +				return -EAGAIN;
> +			}
>  		}
>  	}
>  	desc = hv_get_ring_buffer(outring_info) + old_write;
> @@ -341,7 +343,7 @@ int hv_ringbuffer_write(struct vmbus_channel *channel,
>  	if (channel->rescind) {
>  		if (rqst_id != VMBUS_NO_RQSTOR) {
>  			/* Reclaim request ID to avoid leak of IDs */
> -			vmbus_request_addr(&channel->requestor, rqst_id);
> +			channel->request_addr_callback(channel, rqst_id);
>  		}
>  		return -ENODEV;
>  	}
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index c64cc7639c39c..1a221ce2d6fdc 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -730,7 +730,7 @@ static void netvsc_send_tx_complete(struct net_device *ndev,
>  	int queue_sends;
>  	u64 cmd_rqst;
> 
> -	cmd_rqst = vmbus_request_addr(&channel->requestor, (u64)desc->trans_id);
> +	cmd_rqst = channel->request_addr_callback(channel, (u64)desc->trans_id);
>  	if (cmd_rqst == VMBUS_RQST_ERROR) {
>  		netdev_err(ndev, "Incorrect transaction id\n");
>  		return;
> @@ -790,8 +790,8 @@ static void netvsc_send_completion(struct net_device *ndev,
> 
>  	/* First check if this is a VMBUS completion without data payload */
>  	if (!msglen) {
> -		cmd_rqst = vmbus_request_addr(&incoming_channel->requestor,
> -					      (u64)desc->trans_id);
> +		cmd_rqst = incoming_channel->request_addr_callback(incoming_channel,
> +								   (u64)desc->trans_id);
>  		if (cmd_rqst == VMBUS_RQST_ERROR) {
>  			netdev_err(ndev, "Invalid transaction id\n");
>  			return;
> @@ -1602,6 +1602,8 @@ struct netvsc_device *netvsc_device_add(struct hv_device
> *device,
>  		       netvsc_poll, NAPI_POLL_WEIGHT);
> 
>  	/* Open the channel */
> +	device->channel->next_request_id_callback = vmbus_next_request_id;
> +	device->channel->request_addr_callback = vmbus_request_addr;
>  	device->channel->rqstor_size = netvsc_rqstor_size(netvsc_ring_bytes);
>  	ret = vmbus_open(device->channel, netvsc_ring_bytes,
>  			 netvsc_ring_bytes,  NULL, 0,
> diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
> index 123cc9d25f5ed..ebf34bf3f9075 100644
> --- a/drivers/net/hyperv/rndis_filter.c
> +++ b/drivers/net/hyperv/rndis_filter.c
> @@ -1259,6 +1259,8 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
>  	/* Set the channel before opening.*/
>  	nvchan->channel = new_sc;
> 
> +	new_sc->next_request_id_callback = vmbus_next_request_id;
> +	new_sc->request_addr_callback = vmbus_request_addr;
>  	new_sc->rqstor_size = netvsc_rqstor_size(netvsc_ring_bytes);
>  	ret = vmbus_open(new_sc, netvsc_ring_bytes,
>  			 netvsc_ring_bytes, NULL, 0,
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 6bc5453cea8a7..1c05fabc06b04 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -684,6 +684,62 @@ static void storvsc_change_target_cpu(struct vmbus_channel
> *channel, u32 old,
>  	spin_unlock_irqrestore(&stor_device->lock, flags);
>  }
> 
> +u64 storvsc_next_request_id(struct vmbus_channel *channel, u64 rqst_addr)
> +{
> +	struct storvsc_cmd_request *request =
> +		(struct storvsc_cmd_request *)(unsigned long)rqst_addr;
> +	struct storvsc_device *stor_device;
> +	struct hv_device *device;
> +
> +	device = (channel->primary_channel != NULL) ?
> +		channel->primary_channel->device_obj : channel->device_obj;
> +	if (device == NULL)
> +		return VMBUS_RQST_ERROR;
> +
> +	stor_device = get_out_stor_device(device);
> +	if (stor_device == NULL)
> +		return VMBUS_RQST_ERROR;
> +
> +	if (request == &stor_device->init_request)
> +		return VMBUS_RQST_INIT;
> +	if (request == &stor_device->reset_request)
> +		return VMBUS_RQST_RESET;

Having to get the device and then the stor_device in order to detect the
init_request and reset_request special cases is unfortunate.  So here's
an idea:  The init_request and reset_request are used in a limited number
of specific places in the storvsc driver, and there are unique invocations
of vmbus_sendpacket() in those places.  So rather than pass the address
of the request as the requestID parameter to vmbus_sendpacket(), pass
the sentinel value VMBUS_RQST_INIT or VMBUS_RQST_RESET.  Then this
code can just detect those sentinel values as the rqst_addr input
parameter, and return them.

> +
> +	return blk_mq_unique_tag(request->cmd->request);
> +}
> +
> +u64 storvsc_request_addr(struct vmbus_channel *channel, u64 rqst_id)
> +{
> +	struct storvsc_cmd_request *request;
> +	struct storvsc_device *stor_device;
> +	struct hv_device *device;
> +	struct Scsi_Host *shost;
> +	struct scsi_cmnd *scmnd;
> +
> +	device = (channel->primary_channel != NULL) ?
> +		channel->primary_channel->device_obj : channel->device_obj;
> +	if (device == NULL)
> +		return VMBUS_RQST_ERROR;
> +
> +	stor_device = get_out_stor_device(device);
> +	if (stor_device == NULL)
> +		return VMBUS_RQST_ERROR;
> +
> +	if (rqst_id == VMBUS_RQST_INIT)
> +		return (unsigned long)&stor_device->init_request;
> +	if (rqst_id == VMBUS_RQST_RESET)
> +		return (unsigned long)&stor_device->reset_request;

Unfortunately, the same simplification doesn't work here.  And you need
stor_device anyway to get the scsi_host.

> +
> +	shost = stor_device->host;
> +
> +	scmnd = scsi_host_find_tag(shost, rqst_id);
> +	if (scmnd == NULL)
> +		return VMBUS_RQST_ERROR;
> +
> +	request = (struct storvsc_cmd_request *)(unsigned long)scsi_cmd_priv(scmnd);
> +	return (unsigned long)request;

The casts in the above two lines seem unnecessarily complex.  'request' is never
used as a pointer.  So couldn't the last two lines just be:

	return (unsigned long)scsi_cmd_priv(scmnd);

> +}
> +
>  static void handle_sc_creation(struct vmbus_channel *new_sc)
>  {
>  	struct hv_device *device = new_sc->primary_channel->device_obj;
> @@ -698,11 +754,8 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
> 
>  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
> 
> -	/*
> -	 * The size of vmbus_requestor is an upper bound on the number of requests
> -	 * that can be in-progress at any one time across all channels.
> -	 */
> -	new_sc->rqstor_size = scsi_driver.can_queue;
> +	new_sc->next_request_id_callback = storvsc_next_request_id;
> +	new_sc->request_addr_callback = storvsc_request_addr;
> 
>  	ret = vmbus_open(new_sc,
>  			 storvsc_ringbuffer_size,
> @@ -1255,8 +1308,7 @@ static void storvsc_on_channel_callback(void *context)
>  		struct storvsc_cmd_request *request;
>  		u64 cmd_rqst;
> 
> -		cmd_rqst = vmbus_request_addr(&channel->requestor,
> -					      desc->trans_id);
> +		cmd_rqst = channel->request_addr_callback(channel, desc->trans_id);

Here's another thought:  You don't really need to set the channel request_addr_callback
function and then indirect through it here.  You know the specific function that storvsc
is using, so could call it directly.  The other reason to set request_addr_callback is so
that at the end of hv_ringbuffer_write() you can reclaim an allocated requestID if the
rescind flag is set.  But there's nothing allocated that needs to be reclaimed in the storvsc
case, so leaving request_addr_callback as NULL is OK (but hv_ringbuffer_write would
have to check for the NULL).

Then if you do that, the logic in storvsc_request_addr() can effectively go inline in
here.  And that logic can take advantage of the fact that stor_device is already determined
outside the foreach_vmbus_pkt() loop.  The scsi_host could be calculated outside the loop
as well, leaving the detection of init_request and reset_request, and the call to
scsi_host_find_tag() as the only things to do.

This approach is a bit asymmetrical, but it would save some processing in this interrupt
handling code.   So something to consider.

>  		if (cmd_rqst == VMBUS_RQST_ERROR) {
>  			dev_err(&device->device,
>  				"Incorrect transaction id\n");
> @@ -1290,11 +1342,8 @@ static int storvsc_connect_to_vsp(struct hv_device *device, u32
> ring_size,
> 
>  	memset(&props, 0, sizeof(struct vmstorage_channel_properties));
> 
> -	/*
> -	 * The size of vmbus_requestor is an upper bound on the number of requests
> -	 * that can be in-progress at any one time across all channels.
> -	 */
> -	device->channel->rqstor_size = scsi_driver.can_queue;
> +	device->channel->next_request_id_callback = storvsc_next_request_id;
> +	device->channel->request_addr_callback = storvsc_request_addr;
> 
>  	ret = vmbus_open(device->channel,
>  			 ring_size,
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 2c18c8e768efe..5692ffa60e022 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -779,7 +779,11 @@ struct vmbus_requestor {
> 
>  #define VMBUS_NO_RQSTOR U64_MAX
>  #define VMBUS_RQST_ERROR (U64_MAX - 1)
> +/* NetVSC-specific */

It is netvsc specific at the moment.  But if we harden other
drivers, they are likely to use the same generic requestID
allocator, and hence need the same sentinel value.

>  #define VMBUS_RQST_ID_NO_RESPONSE (U64_MAX - 2)
> +/* StorVSC-specific */
> +#define VMBUS_RQST_INIT (U64_MAX - 2)
> +#define VMBUS_RQST_RESET (U64_MAX - 3)
> 
>  struct vmbus_device {
>  	u16  dev_type;
> @@ -1007,13 +1011,18 @@ struct vmbus_channel {
>  	u32 fuzz_testing_interrupt_delay;
>  	u32 fuzz_testing_message_delay;
> 
> +	/* callback to generate a request ID from a request address */
> +	u64 (*next_request_id_callback)(struct vmbus_channel *channel, u64 rqst_addr);
> +	/* callback to retrieve a request address from a request ID */
> +	u64 (*request_addr_callback)(struct vmbus_channel *channel, u64 rqst_id);
> +
>  	/* request/transaction ids for VMBus */
>  	struct vmbus_requestor requestor;
>  	u32 rqstor_size;
>  };
> 
> -u64 vmbus_next_request_id(struct vmbus_requestor *rqstor, u64 rqst_addr);
> -u64 vmbus_request_addr(struct vmbus_requestor *rqstor, u64 trans_id);
> +u64 vmbus_next_request_id(struct vmbus_channel *channel, u64 rqst_addr);
> +u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id);
> 
>  static inline bool is_hvsock_channel(const struct vmbus_channel *c)
>  {
> --
> 2.25.1

Powered by blists - more mailing lists