netdev - [net-next 07/10] i40e: stop using cmpxchg flow in i40e_set_priv

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Date:   Mon, 26 Mar 2018 14:41:00 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     davem@...emloft.net
Cc:     Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net-next 07/10] i40e: stop using cmpxchg flow in i40e_set_priv_flags()

From: Jacob Keller <jacob.e.keller@...el.com>

Now that the only places which modify flags are either (a) during
initialization prior to creating a netdevice, or (b) while holding the
rtnl lock, we no longer need the cmpxchg64 call in i40e_set_priv_flags.

Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
 drivers/net/ethernet/intel/i40e/i40e_ethtool.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
index 2a9c93091e3d..b974482ff630 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
@@ -4436,21 +4436,12 @@ static int i40e_set_priv_flags(struct net_device *dev, u32 flags)
 		}
 	}
 
-	/* Compare and exchange the new flags into place. If we failed, that
-	 * is if cmpxchg returns anything but the old value, this means that
-	 * something else has modified the flags variable since we copied it
-	 * originally. We'll just punt with an error and log something in the
-	 * message buffer.
-	 *
-	 * This is the point of no return for this function.  We need to have
-	 * checked any discrepancies or misconfigurations and returned
-	 * EOPNOTSUPP before updating pf->flags here.
+	/* Now that we've checked to ensure that the new flags are valid, load
+	 * them into place. Since we only modify flags either (a) during
+	 * initialization or (b) while holding the RTNL lock, we don't need
+	 * anything fancy here.
 	 */
-	if (cmpxchg64(&pf->flags, orig_flags, new_flags) != orig_flags) {
-		dev_warn(&pf->pdev->dev,
-			 "Unable to update pf->flags as it was modified by another thread...\n");
-		return -EAGAIN;
-	}
+	pf->flags = new_flags;
 
 	/* Process any additional changes needed as a result of flag changes.
 	 * The changed_flags value reflects the list of bits that were
-- 
2.14.3