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[67.180.167.114]) by smtp.gmail.com with ESMTPSA id r19-v6sm35196143pgg.39.2018.09.18.07.00.05 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Sep 2018 07:00:06 -0700 (PDT) Subject: Re: [PATCH] bonding: avoid repeated display of same link status change To: Manish Kumar Singh , Eric Dumazet , netdev@vger.kernel.org Cc: Jay Vosburgh , Veaceslav Falico , Andy Gospodarek , "David S. Miller" , linux-kernel@vger.kernel.org References: <20180917072059.32657-1-mk.singh@oracle.com> <33a66a80-22ed-d6b3-f6b2-4463357c5ffa@gmail.com> <78bf3185-fbd1-4a6c-ae32-70da0af2cbb4@default> From: Eric Dumazet Message-ID: <05f57c08-3ebb-7ee5-7ab2-519cb5a70bd8@gmail.com> Date: Tue, 18 Sep 2018 07:00:05 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <78bf3185-fbd1-4a6c-ae32-70da0af2cbb4@default> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/17/2018 10:05 PM, Manish Kumar Singh wrote: > > >> -----Original Message----- >> From: Eric Dumazet [mailto:eric.dumazet@gmail.com] >> Sent: 17 सितम्बर 2018 20:08 >> To: Manish Kumar Singh; netdev@vger.kernel.org >> Cc: Jay Vosburgh; Veaceslav Falico; Andy Gospodarek; David S. Miller; linux- >> kernel@vger.kernel.org >> Subject: Re: [PATCH] bonding: avoid repeated display of same link status >> change >> >> >> >> On 09/17/2018 12:20 AM, mk.singh@oracle.com wrote: >>> From: Manish Kumar Singh >>> >>> When link status change needs to be committed and rtnl lock couldn't be >>> taken, avoid redisplay of same link status change message. >>> >>> Signed-off-by: Manish Kumar Singh >>> --- >>> drivers/net/bonding/bond_main.c | 6 ++++-- >>> include/net/bonding.h | 1 + >>> 2 files changed, 5 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/net/bonding/bond_main.c >> b/drivers/net/bonding/bond_main.c >>> index 217b790d22ed..fb4e3aff1677 100644 >>> --- a/drivers/net/bonding/bond_main.c >>> +++ b/drivers/net/bonding/bond_main.c >>> @@ -2087,7 +2087,7 @@ static int bond_miimon_inspect(struct bonding >> *bond) >>> bond_propose_link_state(slave, BOND_LINK_FAIL); >>> commit++; >>> slave->delay = bond->params.downdelay; >>> - if (slave->delay) { >>> + if (slave->delay && !bond->rtnl_needed) { >>> netdev_info(bond->dev, "link status down for >> %sinterface %s, disabling it in %d ms\n", >>> (BOND_MODE(bond) == >>> BOND_MODE_ACTIVEBACKUP) ? >>> @@ -2127,7 +2127,7 @@ static int bond_miimon_inspect(struct bonding >> *bond) >>> commit++; >>> slave->delay = bond->params.updelay; >>> >>> - if (slave->delay) { >>> + if (slave->delay && !bond->rtnl_needed) { >>> netdev_info(bond->dev, "link status up for >> interface %s, enabling it in %d ms\n", >>> slave->dev->name, >>> ignore_updelay ? 0 : >>> @@ -2301,9 +2301,11 @@ static void bond_mii_monitor(struct >> work_struct *work) >>> if (!rtnl_trylock()) { >>> delay = 1; >>> should_notify_peers = false; >>> + bond->rtnl_needed = true; >> >> How can you set a shared variable with no synchronization ? > Thanks Eric for reviewing the patch. rtnl_needed is not a shared variable, it is part of bonding structure, that is one per bonding driver instance. There can't be two parallel instances of bond_miimon_inspect for a single  bonding driver instance at any given point of time. and only bond_miimon_inspect updates it. That’s why I think there is no need of any synchronization here. > > If rtnl_trylock() can not grab RTNL, there is no way the current thread can set the variable without a race, if the word including rtnl_needed is shared by other fields in the structure. Your patch adds a subtle possibility of future bugs, even if it runs fine today. Do not pave the way for future bugs, make your code robust, please.