netdev - [PATCH AUTOSEL 5.15 19/36] netpoll: Remove 4s sleep during carrier detection

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Message-Id: <20230226144845.827893-19-sashal@kernel.org>
Date:   Sun, 26 Feb 2023 09:48:27 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Breno Leitao <leitao@...ian.org>,
        Michael van der Westhuizen <rmikey@...a.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com,
        wsa+renesas@...g-engineering.com, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 19/36] netpoll: Remove 4s sleep during carrier detection

From: Breno Leitao <leitao@...ian.org>

[ Upstream commit d8afe2f8a92d2aac3df645772f6ee61b0b2fc147 ]

This patch removes the msleep(4s) during netpoll_setup() if the carrier
appears instantly.

Here are some scenarios where this workaround is counter-productive in
modern ages:

Servers which have BMC communicating over NC-SI via the same NIC as gets
used for netconsole. BMC will keep the PHY up, hence the carrier
appearing instantly.

The link is fibre, SERDES getting sync could happen within 0.1Hz, and
the carrier also appears instantly.

Other than that, if a driver is reporting instant carrier and then
losing it, this is probably a driver bug.

Reported-by: Michael van der Westhuizen <rmikey@...a.com>
Signed-off-by: Breno Leitao <leitao@...ian.org>
Link: https://lore.kernel.org/r/20230125185230.3574681-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/core/netpoll.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index edfc0f8011f88..0fc64f536db01 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -682,7 +682,7 @@ int netpoll_setup(struct netpoll *np)
 	}
 
 	if (!netif_running(ndev)) {
-		unsigned long atmost, atleast;
+		unsigned long atmost;
 
 		np_info(np, "device %s not up yet, forcing it\n", np->dev_name);
 
@@ -694,7 +694,6 @@ int netpoll_setup(struct netpoll *np)
 		}
 
 		rtnl_unlock();
-		atleast = jiffies + HZ/10;
 		atmost = jiffies + carrier_timeout * HZ;
 		while (!netif_carrier_ok(ndev)) {
 			if (time_after(jiffies, atmost)) {
@@ -704,15 +703,6 @@ int netpoll_setup(struct netpoll *np)
 			msleep(1);
 		}
 
-		/* If carrier appears to come up instantly, we don't
-		 * trust it and pause so that we don't pump all our
-		 * queued console messages into the bitbucket.
-		 */
-
-		if (time_before(jiffies, atleast)) {
-			np_notice(np, "carrier detect appears untrustworthy, waiting 4 seconds\n");
-			msleep(4000);
-		}
 		rtnl_lock();
 	}
 
-- 
2.39.0