netdev - [PATCH net 1/3] i40e: fix endless loop under rtnl

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Message-Id: <20211006165659.2298400-2-anthony.l.nguyen@intel.com>
Date:   Wed,  6 Oct 2021 09:56:57 -0700
From:   Tony Nguyen <anthony.l.nguyen@...el.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     Jiri Benc <jbenc@...hat.com>, netdev@...r.kernel.org,
        anthony.l.nguyen@...el.com, sassmann@...hat.com,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Dave Switzer <david.switzer@...el.com>
Subject: [PATCH net 1/3] i40e: fix endless loop under rtnl

From: Jiri Benc <jbenc@...hat.com>

The loop in i40e_get_capabilities can never end. The problem is that
although i40e_aq_discover_capabilities returns with an error if there's
a firmware problem, the returned error is not checked. There is a check for
pf->hw.aq.asq_last_status but that value is set to I40E_AQ_RC_OK on most
firmware problems.

When i40e_aq_discover_capabilities encounters a firmware problem, it will
encounter the same problem on its next invocation. As the result, the loop
becomes endless. We hit this with I40E_ERR_ADMIN_QUEUE_TIMEOUT but looking
at the code, it can happen with a range of other firmware errors.

I don't know what the correct behavior should be: whether the firmware
should be retried a few times, or whether pf->hw.aq.asq_last_status should
be always set to the encountered firmware error (but then it would be
pointless and can be just replaced by the i40e_aq_discover_capabilities
return value). However, the current behavior with an endless loop under the
rtnl mutex(!) is unacceptable and Intel has not submitted a fix, although we
explained the bug to them 7 months ago.

This may not be the best possible fix but it's better than hanging the whole
system on a firmware bug.

Fixes: 56a62fc86895 ("i40e: init code and hardware support")
Tested-by: Stefan Assmann <sassmann@...hat.com>
Signed-off-by: Jiri Benc <jbenc@...hat.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
Tested-by: Dave Switzer <david.switzer@...el.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
 drivers/net/ethernet/intel/i40e/i40e_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index 2f20980dd9a5..b5b984754ec9 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -10113,7 +10113,7 @@ static int i40e_get_capabilities(struct i40e_pf *pf,
 		if (pf->hw.aq.asq_last_status == I40E_AQ_RC_ENOMEM) {
 			/* retry with a larger buffer */
 			buf_len = data_size;
-		} else if (pf->hw.aq.asq_last_status != I40E_AQ_RC_OK) {
+		} else if (pf->hw.aq.asq_last_status != I40E_AQ_RC_OK || err) {
 			dev_info(&pf->pdev->dev,
 				 "capability discovery failed, err %s aq_err %s\n",
 				 i40e_stat_str(&pf->hw, err),
-- 
2.31.1