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

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