linux-kernel - Re: [PATCH] ibmvnic: remove excessive irqsave

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Message-Id: <753DD123-9E78-4270-B6D8-81A8D07B1FA0@linux.vnet.ibm.com>
Date:   Fri, 5 Mar 2021 00:04:27 -0600
From:   Lijun Pan <ljp@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     angkery <angkery@....com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org,
        Dany Madden <drt@...ux.ibm.com>, Lijun Pan <ljp@...ux.ibm.com>,
        Sukadev Bhattiprolu <sukadev@...ux.ibm.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Junlin Yang <yangjunlin@...ong.com>
Subject: Re: [PATCH] ibmvnic: remove excessive irqsave



> On Mar 4, 2021, at 11:49 PM, Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
> 
> 
> Le 05/03/2021 à 02:43, angkery a écrit :
>> From: Junlin Yang <yangjunlin@...ong.com>
>> ibmvnic_remove locks multiple spinlocks while disabling interrupts:
>> spin_lock_irqsave(&adapter->state_lock, flags);
>> spin_lock_irqsave(&adapter->rwi_lock, flags);
>> there is no need for the second irqsave,since interrupts are disabled
>> at that point, so remove the second irqsave:
> 
> The problème is not that there is no need. The problem is a lot more serious:
> As reported by coccinella, the second _irqsave() overwrites the value saved in 'flags' by the first _irqsave, therefore when the second _irqrestore comes, the value in 'flags' is not valid, the value saved by the first _irqsave has been lost. This likely leads to IRQs remaining disabled, which is _THE_ problem really.

That does sounds like a more serious functional problem than coccinella check.
Thanks for your explanation.

> 
>> spin_lock_irqsave(&adapter->state_lock, flags);
>> spin_lock(&adapter->rwi_lock);
>> Generated by: ./scripts/coccinelle/locks/flags.cocci
>> ./drivers/net/ethernet/ibm/ibmvnic.c:5413:1-18:
>> ERROR: nested lock+irqsave that reuses flags from line 5404.
>> Signed-off-by: Junlin Yang <yangjunlin@...ong.com>
>> ---
>>  drivers/net/ethernet/ibm/ibmvnic.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
>> index 2464c8a..a52668d 100644
>> --- a/drivers/net/ethernet/ibm/ibmvnic.c
>> +++ b/drivers/net/ethernet/ibm/ibmvnic.c
>> @@ -5408,9 +5408,9 @@ static void ibmvnic_remove(struct vio_dev *dev)
>>  	 * after setting state, so __ibmvnic_reset() which is called
>>  	 * from the flush_work() below, can make progress.
>>  	 */
>> -	spin_lock_irqsave(&adapter->rwi_lock, flags);
>> +	spin_lock(&adapter->rwi_lock);
>>  	adapter->state = VNIC_REMOVING;
>> -	spin_unlock_irqrestore(&adapter->rwi_lock, flags);
>> +	spin_unlock(&adapter->rwi_lock);
>>    	spin_unlock_irqrestore(&adapter->state_lock, flags);
>>