RE: [PATCH v3 2/2] IB/mad: Use ID allocator routines to allocate agent number

[Matthew Wilcox <mawilcox@microsoft.com>]

Why do you need the ID to increment like this?  Why can't you just use a unique ID?

> -----Original Message-----
> From: Hans Westgaard Ry [mailto:hans.westgaard.ry@oracle.com]
> Sent: Thursday, June 7, 2018 7:15 AM
> To: Doug Ledford <dledford@redhat.com>; Jason Gunthorpe <jgg@ziepe.ca>;
> Hakon Bugge <haakon.bugge@oracle.com>; Parav Pandit
> <parav@mellanox.com>; Jack Morgenstein <jackm@dev.mellanox.co.il>; Pravin
> Shedge <pravin.shedge4linux@gmail.com>; Matthew Wilcox
> <mawilcox@microsoft.com>; Andrew Morton <akpm@linux-foundation.org>;
> Jeff Layton <jlayton@kernel.org>; Wei Wang <wei.w.wang@intel.com>; Chris
> Mi <chrism@mellanox.com>; Eric Biggers <ebiggers@google.com>; Rasmus
> Villemoes <linux@rasmusvillemoes.dk>; Mel Gorman
> <mgorman@techsingularity.net>; linux-rdma@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: [PATCH v3 2/2] IB/mad: Use ID allocator routines to allocate agent
> number
> 
> The agent TID is a 64 bit value split in two dwords.  The least
> significant dword is the TID running counter. The most significant
> dword is the agent number. In the CX-3 shared port model, the mlx4
> driver uses the most significant byte of the agent number to store the
> slave number, making agent numbers greater and equal to 2^24 (3 bytes)
> unusable.  The current codebase uses a variable which is incremented
> atomically for each new agent number giving too large agent numbers
> over time.  The IDA set of functions are used instead of the simple
> counter approach. This allows re-use of agent numbers.
> 
> The signature of the bug is a MAD layer that stops working and the
> console is flooded with messages like:
>  mlx4_ib: egress mad has non-null tid msb:1 class:4 slave:0
> 
> Signed-off-by: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>
> ---
>  drivers/infiniband/core/mad.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/core/mad.c b/drivers/infiniband/core/mad.c
> index b28452a55a08..c01a2d63ffa2 100644
> --- a/drivers/infiniband/core/mad.c
> +++ b/drivers/infiniband/core/mad.c
> @@ -41,6 +41,7 @@
>  #include <linux/slab.h>
>  #include <linux/module.h>
>  #include <linux/security.h>
> +#include <linux/idr.h>
>  #include <rdma/ib_cache.h>
> 
>  #include "mad_priv.h"
> @@ -59,8 +60,7 @@ module_param_named(recv_queue_size,
> mad_recvq_size, int, 0444);
>  MODULE_PARM_DESC(recv_queue_size, "Size of receive queue in number of
> work requests");
> 
>  static struct list_head ib_mad_port_list;
> -static atomic_t ib_mad_client_id = ATOMIC_INIT(0);
> -
> +static DEFINE_IDA(ib_mad_client_ids);
>  /* Port list lock */
>  static DEFINE_SPINLOCK(ib_mad_port_list_lock);
> 
> @@ -212,7 +212,7 @@ struct ib_mad_agent *ib_register_mad_agent(struct
> ib_device *device,
>  	int ret2, qpn;
>  	unsigned long flags;
>  	u8 mgmt_class, vclass;
> -
> +	u32 ib_mad_client_id;
>  	/* Validate parameters */
>  	qpn = get_spl_qp_index(qp_type);
>  	if (qpn == -1) {
> @@ -375,9 +375,19 @@ struct ib_mad_agent *ib_register_mad_agent(struct
> ib_device *device,
>  		ret = ERR_PTR(ret2);
>  		goto error4;
>  	}
> +	ib_mad_client_id = ida_simple_get_cyclic(&ib_mad_client_ids,
> +						1,
> +						BIT(24) - 1,
> +						GFP_KERNEL);
> +	if (ib_mad_client_id < 0) {
> +		pr_err("Couldn't allocate agent tid; errcode: %#x\n",
> +			ib_mad_client_id);
> +		ret = ERR_PTR(ib_mad_client_id);
> +		goto error4;
> +	}
> +	mad_agent_priv->agent.hi_tid = ib_mad_client_id;
> 
>  	spin_lock_irqsave(&port_priv->reg_lock, flags);
> -	mad_agent_priv->agent.hi_tid =
> atomic_inc_return(&ib_mad_client_id);
> 
>  	/*
>  	 * Make sure MAD registration (if supplied)
> @@ -428,6 +438,8 @@ struct ib_mad_agent *ib_register_mad_agent(struct
> ib_device *device,
>  error5:
>  	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
>  	ib_mad_agent_security_cleanup(&mad_agent_priv->agent);
> +	ida_simple_remove(&ib_mad_client_ids, ib_mad_client_id);
> +
>  error4:
>  	kfree(reg_req);
>  error3:
> @@ -576,6 +588,7 @@ static void unregister_mad_agent(struct
> ib_mad_agent_private *mad_agent_priv)
>  {
>  	struct ib_mad_port_private *port_priv;
>  	unsigned long flags;
> +	u32 ib_mad_client_id;
> 
>  	/* Note that we could still be handling received MADs */
> 
> @@ -587,6 +600,8 @@ static void unregister_mad_agent(struct
> ib_mad_agent_private *mad_agent_priv)
>  	port_priv = mad_agent_priv->qp_info->port_priv;
>  	cancel_delayed_work(&mad_agent_priv->timed_work);
> 
> +	ib_mad_client_id = mad_agent_priv->agent.hi_tid;
> +
>  	spin_lock_irqsave(&port_priv->reg_lock, flags);
>  	remove_mad_reg_req(mad_agent_priv);
>  	list_del(&mad_agent_priv->agent_list);
> @@ -602,6 +617,7 @@ static void unregister_mad_agent(struct
> ib_mad_agent_private *mad_agent_priv)
> 
>  	kfree(mad_agent_priv->reg_req);
>  	kfree(mad_agent_priv);
> +	ida_simple_remove(&ib_mad_client_ids, ib_mad_client_id);
>  }
> 
>  static void unregister_mad_snoop(struct ib_mad_snoop_private
> *mad_snoop_priv)
> @@ -3347,4 +3363,5 @@ int ib_mad_init(void)
>  void ib_mad_cleanup(void)
>  {
>  	ib_unregister_client(&mad_client);
> +	ida_destroy(&ib_mad_client_ids);
>  }
> --
> 2.14.3