User SIW fails matching device

[Potnuri Bharat Teja <bharat@chelsio.com>]

Hi all,
I observe the following behavior on one of my machines configured for siw.

Issue:
SIW device gets wrong device ops (HW/real rdma driver device ops) instead of
siw device ops due to improper device matching.

Root-cause:
In libibverbs, during user cma initialisation, for each entry from the driver 
list, sysfs device is checked for matching name or device.
If the siw/rxe driver is at the head of the list, then sysfs device matches 
properly with the corresponding siw driver and gets the corresponding siw/rxe 
device ops. Now, If the siw/rxe driver is after the real HW driver cxgb4/mlx5 
respectively in the driver list, then siw sysfs device matches pci device and 
wrongly gets the device ops of HW driver (cxgb4/mlx5).

Below debug prints from verbs_register_driver() and driver_list entries, where 
siw is after cxgb4. I see verbs alloc context landing in cxgb4_alloc_context 
instead of siw_alloc_context, thus breaking user siw.

<debug> verbs_register_driver_22: 184: driver 0x176e370
<debug> verbs_register_driver_22: 185: name ipathverbs
<debug> verbs_register_driver_22: 184: driver 0x176f6a0
<debug> verbs_register_driver_22: 185: name cxgb4
<debug> verbs_register_driver_22: 184: driver 0x176fd50
<debug> verbs_register_driver_22: 185: name cxgb3
<debug> verbs_register_driver_22: 184: driver 0x1777020
<debug> verbs_register_driver_22: 185: name rxe
<debug> verbs_register_driver_22: 184: driver 0x1770a30
<debug> verbs_register_driver_22: 185: name siw
<debug> verbs_register_driver_22: 184: driver 0x1771120
<debug> verbs_register_driver_22: 185: name mlx4
<debug> verbs_register_driver_22: 184: driver 0x1771990
<debug> verbs_register_driver_22: 185: name mlx5
<debug> verbs_register_driver_22: 184: driver 0x1771ff0
<debug> verbs_register_driver_22: 185: name efa

<debug> try_drivers: 372: driver 0x176e370, sysfs_dev 0x1776b20, name: ipathverbs
<debug> try_drivers: 372: driver 0x176f6a0, sysfs_dev 0x1776b20, name: cxgb4
<debug> try_drivers: 372: driver 0x176fd50, sysfs_dev 0x1776b20, name: cxgb3
<debug> try_drivers: 372: driver 0x1777020, sysfs_dev 0x1776b20, name: rxe
<debug> try_drivers: 372: driver 0x1770a30, sysfs_dev 0x1776b20, name: siw
<debug> try_drivers: 372: driver 0x1771120, sysfs_dev 0x1776b20, name: mlx4
<debug> try_drivers: 372: driver 0x1771990, sysfs_dev 0x1776b20, name: mlx5
<debug> try_drivers: 372: driver 0x1771ff0, sysfs_dev 0x1776b20, name: efa

Proposed fix:
I have the below fix that works. It adds siw/rxe driver to the HEAD of the 
driver list and the rest to the tail. I am not sure if this fix is the ideal 
one, so I am attaching it to this mail.

diff --git a/libibverbs/init.c b/libibverbs/init.c
index 930d91811ca9..e44f0d743063 100644
--- a/libibverbs/init.c
+++ b/libibverbs/init.c
@@ -182,7 +182,10 @@ void verbs_register_driver(const struct verbs_device_ops *ops)

	driver->ops = ops;

-       list_add_tail(&driver_list, &driver->entry);
+       if (!strcmp(ops->name, "siw") || !strcmp(ops->name, "rxe"))
+               list_add(&driver_list, &driver->entry);
+       else
+               list_add_tail(&driver_list, &driver->entry);
 }
---

Thanks,
Bharat