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

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Message-ID: <20210305150325.0000286b.angkery@163.com>
Date:   Fri, 5 Mar 2021 15:03:25 +0800
From:   angkery <angkery@....com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        drt@...ux.ibm.com, ljp@...ux.ibm.com, sukadev@...ux.ibm.com,
        davem@...emloft.net, 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 Fri, 5 Mar 2021 06:49:14 +0100
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.
> 

Thank you for explaining the real problem.
I will update the commit information with your description.


> > 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);
> >   
> >