RE: [EXTERNAL] Re: [PATCH net v3] net: mana: Clear RDMA teardown and suspend state in mana_rdma_probe()

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Critical: 0 · High: 0 · Medium: 1 · Low: 0

- [Medium] In mana_rdma_probe()
  (drivers/net/ethernet/microsoft/mana/mana_en.c:4296) the servicing.

--

net: mana: Clear RDMA teardown and suspend state in mana_rdma_probe()

mana_rdma_remove() sets gd->rdma_teardown and nothing ever clears it, so
after the first hardware service reset every GDMA_EQE_HWC_SOC_SERVICE
event returns early.  This patch clears gd->is_suspended and re-opens the
gate with smp_store_release() in mana_rdma_probe(), paired with a new
smp_load_acquire() in mana_rdma_service_handle().

quoted

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c

b/drivers/net/ethernet/microsoft/mana/mana_en.c
index 7a1ac853e3ab..d8e847df7a44 100644

--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c

@@ -3983,7 +3983,8 @@ static void mana_rdma_service_handle(struct

work_struct *work)

quoted

 	struct device *dev = gd->gdma_context->dev;
 	int ret;

-	if (READ_ONCE(gd->rdma_teardown))
+	/* Pairs with the smp_store_release() in mana_rdma_probe(). */
+	if (smp_load_acquire(&gd->rdma_teardown))
 		goto out;

 	switch (serv_work->event) {

[ ... ]

quoted

@@ -4279,6 +4280,21 @@ int mana_rdma_probe(struct gdma_dev *gd)
 	if (err)
 		return err;

+	/* Clear the state left by a previous mana_rdma_remove() so

servicing

quoted

+	 * events are handled again after a reset cycle.
+	 */
+	gd->is_suspended = false;
+
+	/* Publish is_suspended before re-opening the gate, so the handler
+	 * cannot observe an open gate with a stale is_suspended.  Pairs
+	 * with the smp_load_acquire() in mana_rdma_service_handle().

This

quoted

+	 * matters on the reset path, where mana_rdma_remove() closed the
+	 * gate and drained the workqueue; on the initial probe path the
+	 * gate was never closed and both flags are already clear.  It does
+	 * not order gd->adev, which add_adev() publishes below.
+	 */
+	smp_store_release(&gd->rdma_teardown, false);
+
 	err = add_adev(gd, "rdma");
 	if (err)
 		mana_gd_deregister_device(gd);

[Severity: Medium]

Would it be better to open the gate after add_adev() succeeds rather than
before it?

As written, the store that re-enables the handler happens while gd->adev is
still NULL from the remove half of the reset cycle.  The publication happens
later, at the end of add_adev():

drivers/net/ethernet/microsoft/mana/mana_en.c:add_adev() {
	...
	ret = auxiliary_device_add(adev);
	if (ret)
		goto add_fail;

	gd->adev = adev;
	...
}

A GDMA_SERVICE_TYPE_RDMA_SUSPEND handled in that window passes the
gate and then hits the gd->adev test in mana_rdma_service_handle():

	case GDMA_SERVICE_TYPE_RDMA_SUSPEND:
		if (!gd->adev || gd->is_suspended)
			break;

		remove_adev(gd);
		gd->is_suspended = true;
		break;

so the suspend request is discarded, probe finishes with a live aux device
and is_suspended == false, and the matching RESUME is then also swallowed
by the "if (!gd->is_suspended) break;" test.  Is the resulting state (host asked
for a quiesce, RDMA aux device still live) recoverable without another reset?

Is the concurrency here real on the reset path?  From what I can follow, the
probe runs from system_wq while the handler runs on gc->service_wq:

mana_schedule_serv_work()
	schedule_work(&mns_wk->serv_work)   /* system_wq */
	  mana_serv_reset()
	    mana_gd_suspend() -> mana_rdma_remove()
	    mana_gd_resume()  -> mana_gd_setup()
	                      -> mana_probe()
	                      -> mana_rdma_probe()

and mana_gd_resume() calls mana_gd_setup() first, which re-creates
gc->service_wq, re-arms the HWC IRQs, re-creates the HW channel and
re-detects devices so gc->mana_ib.dev_id.type is valid again, all before
mana_rdma_probe() runs.  So an event arriving during probe reaches
mana_hwc_init_event_handler() -> mana_rdma_service_event() ->
queue_work(gc->service_wq) and mana_rdma_service_handle() can execute
on another CPU while mana_rdma_probe() is still in add_adev().  Since the
event timing is driven by the host, is that window reachable in practice?

In the opposite interleaving, the handler reads gd->adev with a plain load
and immediately destroys the object through remove_adev()
(auxiliary_device_delete/uninit, mana_adev_idx_free) while probe is still
finishing.  The new acquire load only orders is_suspended against the
release; the "gd->adev = adev;" store has no release pairing with the
handler's load.  Would publishing gd->adev with release semantics, or
moving the smp_store_release() below a successful add_adev(), cover this
too?

There is also the question of what rdma_teardown now is.  Before this patch
it was a write-once teardown flag; with the clear in mana_rdma_probe() it
becomes a gate that mana_rdma_remove() closes on entry:

	WRITE_ONCE(gd->rdma_teardown, true);

	if (gc->service_wq)
		flush_workqueue(gc->service_wq);

and that mana_rdma_probe() re-opens on the way back in.  That is a flag
guarding a code region rather than expressing device state.  Would a mutex
held across mana_rdma_probe(), mana_rdma_remove() and
mana_rdma_service_handle() be a better fit here, since it would also remove
the window the comment documents instead of describing it?

This is a pre-existing issue, not introduced by this patch.

The concurrency is possible: reset/probe and RDMA servicing run on different workqueues, and  GC_IN_SERVICE  does not serialize them.

The underlying probe-window issue already exists before this patch. On initial probe,  gc  is zero-initialized, so  rdma_teardown  is clear.  mana_gd_setup()  enables event processing and detects the RDMA device before  mana_rdma_probe()  publishes  gd->adev . A SUSPEND processed then already encounters:

if (!gd->adev || gd->is_suspended)
        break;

This patch fixes a different problem: after reset,  rdma_teardown  previously remained set permanently, discarding all subsequent servicing events. It also clears stale  is_suspended  to prevent a later RESUME from adding a duplicate auxiliary device. Reopening the gate makes the existing probe-window race reachable after reset too; the patch does not resolve that race.

Moving the release store after successful  add_adev()  would improve publication ordering on the reset path. However, it would not preserve the SUSPEND request: a handler observing the closed gate executes  goto out  and frees the work item without retrying. Publishing  gd->adev  with release/acquire semantics alone likewise would not prevent a handler from observing NULL before publication.

There is no automatic replay of the missed SUSPEND. A later SUSPEND can still be processed, but the matching RESUME cannot retroactively provide the missed quiescence.

I agree that proper serialization, or retaining pending events, is needed to close this existing window. A mutex implementation must cover initialization before servicing can run and must not hold the handler's mutex across  flush_workqueue() . That is separate from restoring servicing after reset.

--
Sashiko AI
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