Re: [PATCH] RDMA/cm: add timeout to cm_destroy_id wait

[Manjunath Patil <manjunath.b.patil@oracle.com>]

On 3/8/24 6:18 AM, Jason Gunthorpe wrote:
> On Thu, Mar 07, 2024 at 04:55:53PM -0800, Manjunath Patil wrote:
>> Add timeout to cm_destroy_id, so that userspace can trigger any data
>> collection that would help in analyzing the cause of delay in destroying
>> the cm_id.
>>
>> New noinline function helps dtrace/ebpf programs to hook on to it.
>> Existing functionality isn't changed except triggering a probe-able new
>> function at every timeout interval.
>>
>> We have seen cases where CM messages stuck with MAD layer (either due to
>> software bug or faulty HCA), leading to cm_id getting stuck in the
>> following call stack. This patch helps in resolving such issues faster.
>>
>> kernel: ... INFO: task XXXX:56778 blocked for more than 120 seconds.
>> ...
>> 	Call Trace:
>> 	__schedule+0x2bc/0x895
>> 	schedule+0x36/0x7c
>> 	schedule_timeout+0x1f6/0x31f
>>   	? __slab_free+0x19c/0x2ba
>> 	wait_for_completion+0x12b/0x18a
>> 	? wake_up_q+0x80/0x73
>> 	cm_destroy_id+0x345/0x610 [ib_cm]
>> 	ib_destroy_cm_id+0x10/0x20 [ib_cm]
>> 	rdma_destroy_id+0xa8/0x300 [rdma_cm]
>> 	ucma_destroy_id+0x13e/0x190 [rdma_ucm]
>> 	ucma_write+0xe0/0x160 [rdma_ucm]
>> 	__vfs_write+0x3a/0x16d
>> 	vfs_write+0xb2/0x1a1
>> 	? syscall_trace_enter+0x1ce/0x2b8
>> 	SyS_write+0x5c/0xd3
>> 	do_syscall_64+0x79/0x1b9
>> 	entry_SYSCALL_64_after_hwframe+0x16d/0x0
>>
>> Orabug: 36280065
>>
>> Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
>> ---
>>   drivers/infiniband/core/cm.c | 20 +++++++++++++++++++-
>>   1 file changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
>> index ff58058aeadc..00a16b08c7e2 100644
>> --- a/drivers/infiniband/core/cm.c
>> +++ b/drivers/infiniband/core/cm.c
>> @@ -34,6 +34,7 @@ MODULE_AUTHOR("Sean Hefty");
>>   MODULE_DESCRIPTION("InfiniBand CM");
>>   MODULE_LICENSE("Dual BSD/GPL");
>>   
>> +static unsigned long cm_destroy_id_wait_timeout_sec = 10;
> 
> Don't need this to be a variable, just make it a #define
sure. I will send v3 with this change.
> 
>>   static const char * const ibcm_rej_reason_strs[] = {
>>   	[IB_CM_REJ_NO_QP]			= "no QP",
>>   	[IB_CM_REJ_NO_EEC]			= "no EEC",
>> @@ -1025,10 +1026,20 @@ static void cm_reset_to_idle(struct cm_id_private *cm_id_priv)
>>   	}
>>   }
>>   
>> +static noinline void cm_destroy_id_wait_timeout(struct ib_cm_id *cm_id)
>> +{
>> +	struct cm_id_private *cm_id_priv;
>> +
>> +	cm_id_priv = container_of(cm_id, struct cm_id_private, id);
>> +	pr_err("%s: cm_id=%p timed out. state=%d refcnt=%d\n", __func__,
>> +	       cm_id, cm_id->state, refcount_read(&cm_id_priv->refcount));
>> +}
> 
> WARN_ON? Is the backtrace valuable?
No. I would prefer just pr_err to avoid noise if there are multiple cm_ids are stuck due to any lower layer issue.

Thank you for your feedback.

-Manjunath
> 
> Jason