quoted

quoted

Remove the complicated logic to free the cm_id resources in iw_cm event
handlers vs when an application thread destroys the device.  I'm not sure
why this code was written, but simply allowing the last deref to free
the memory is cleaner.  It also prevents a deadlock when applications
try to destroy cm_id's in their cm event handler function.

The description here is misleading. we can never destroy the cm_id
inside the cm_id handler. Also, I don't think the deadlock was on cm_id
removal but rather on the qp referenced by the cm_id. I think the change
log can be improved.

I'll reword it.

The nvme unplug handler does indeed destroy all the qps -and- cm_ids used for
the controllers for this device, with the exception of the cm_id handling the
event.  That is what causes this deadlock.  Once I fixed iw_cxgb4 (in patch 2)
to not block until the refcnt reaches 0 in c4iw_destroy_qp(), I then hit the
block in iw_destroy_cm_id() which deadlocks the process due to the iw_cm worker
thread already stuck trying to post an event to the rdma_cm for the cm_id
handling the event.  

Perhaps I should describe the deadlock in detail like I did in the email threads
leading up to this series?

While I'm rambling, there is still a condition that probably needs to be
addressed:  if the application event handler function disconnects the cm_id that
is handling the event, the iw_cm workq thread gets stuck posting a
IW_CM_EVENT_CLOSE to rdma_cm.  So the iw_cm workq thread is stuck in
cm_close_handler() calling cm_id_priv->id.cm_handler() which is cma_iw_handler()
which is blocked in cma_disable_callback() because the application is currently
running its event handler for this cm_id.  This block is released when the
application returns from its event handler function.  

But maybe cma_iw_handler() should queue the event if it cannot deliver it, vs
blocking the iw_cm workq thread?   

Steve.




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