linux-kernel - Re: [PATCH for-next] RDMA/cm: Rate limit destroy CM ID timeout error message

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Message-ID: <49A8CE60-DC8E-43F7-9620-D4D5F8EB2A08@oracle.com>
Date: Thu, 16 Oct 2025 15:25:15 +0000
From: Haakon Bugge <haakon.bugge@...cle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Sean Hefty <shefty@...dia.com>, Jacob Moroni <jmoroni@...gle.com>,
        Leon
 Romanovsky <leon@...nel.org>,
        Vlad Dumitrescu <vdumitrescu@...dia.com>,
        Or
 Har-Toov <ohartoov@...dia.com>,
        Manjunath Patil
	<manjunath.b.patil@...cle.com>,
        OFED mailing list
	<linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH for-next] RDMA/cm: Rate limit destroy CM ID timeout error
 message

> On 15 Oct 2025, at 20:45, Jason Gunthorpe <jgg@...pe.ca> wrote:
> 
> On Wed, Oct 15, 2025 at 06:34:33PM +0000, Sean Hefty wrote:
>>>> With this hack, running cmtime with 10.000 connections in loopback,
>>>> the "cm_destroy_id_wait_timeout: cm_id=000000007ce44ace timed out.
>>>> state 6 -> 0, refcnt=1" messages are indeed produced. Had to kill
>>>> cmtime because it was hanging, and then it got defunct with the
>>>> following stack:
>>> 
>>> Seems like a bug, it should not hang forever if a MAD is lost..
>> 
>> The hack skipped calling ib_post_send.  But the result of that is a
>> completion is never written to the CQ.

Which is exactly the behaviour I see when the VF gets "whacked". This is from a system without the reproducer hack. Looking at the netdev detected TX timeout:

mlx5_core 0000:af:00.2 ens4f2: TX timeout detected
mlx5_core 0000:af:00.2 ens4f2: TX timeout on queue: 0, SQ: 0xe31ee, CQ: 0x484, SQ Cons: 0x0 SQ Prod: 0x7, usecs since last trans: 18439000
mlx5_core 0000:af:00.2 ens4f2: EQ 0x7: Cons = 0x3ded47a, irqn = 0x197

(I get tons of the like)

There are two points here. All of them has "SQ Cons: 0x0", which to me implies that no TX CQE has ever been polled for any of them.

The other point is that we do _not_ see "Recovered %d eqes on EQ 0x%x" (which is because mlx5_eq_poll_irq_disabled() always returns zero), which means that either a) no CQE has been generated by the HCA or b) a CQE has been generated but no corresponding EQE has been written to the EQ.

>>  The state machine or
>> reference counting is likely waiting for the completion, so it knows
>> that HW is done trying to access the buffer.
> 
> That does make sense, it has to immediately trigger the completion to
> be accurate. A better test would be to truncate the mad or something
> so it can't be rx'd

As argued above, I think my reproducer hack is sound and to the point.

I will raise an NVIDIA ticket as to why the VF gets into this "whacked" state. But, since Google has encountered this, we have one customer, and I am able to repro this situation (without my hack) in 1-3 days running on a single server, do we expect the RDMA stack to handle this situation?

Thxs, Håkon