netdev - Re: [PATCH] ibmvnic: remove excessive irqsave

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Date:   Fri, 5 Mar 2021 06:49:14 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     angkery <angkery@....com>, 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
Cc:     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



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.

> 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);
>   
>