netdev - Re: [PATCH net] net: igmp: increase size of mr_ifc

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Date:   Wed, 11 Aug 2021 13:14:46 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] net: igmp: increase size of mr_ifc_count

On Wed, Aug 11, 2021 at 12:57:15PM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Some arches support cmpxchg() on 4-byte and 8-byte only.
> Increase mr_ifc_count width to 32bit to fix this problem.
> 
> Fixes: 4a2b285e7e10 ("net: igmp: fix data-race in igmp_ifc_timer_expire()")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Guenter Roeck <linux@...ck-us.net>

This patch fixes the build problems I had observed.

Tested-by: Guenter Roeck <linux@...ck-us.net>

Thanks,
Guenter

> ---
>  include/linux/inetdevice.h | 2 +-
>  net/ipv4/igmp.c            | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
> index 53aa0343bf694cb817e00ff597b52ce046e29d2c..aaf4f1b4c277c4ad38e1f0742bb480d3bb003287 100644
> --- a/include/linux/inetdevice.h
> +++ b/include/linux/inetdevice.h
> @@ -41,7 +41,7 @@ struct in_device {
>  	unsigned long		mr_qri;		/* Query Response Interval */
>  	unsigned char		mr_qrv;		/* Query Robustness Variable */
>  	unsigned char		mr_gq_running;
> -	unsigned char		mr_ifc_count;
> +	u32			mr_ifc_count;
>  	struct timer_list	mr_gq_timer;	/* general query timer */
>  	struct timer_list	mr_ifc_timer;	/* interface change timer */
>  
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index a51360087b19845a28408c827032e08dabf99838..00576bae183d30518e376ad3846d4fe6025aaea7 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -803,7 +803,7 @@ static void igmp_gq_timer_expire(struct timer_list *t)
>  static void igmp_ifc_timer_expire(struct timer_list *t)
>  {
>  	struct in_device *in_dev = from_timer(in_dev, t, mr_ifc_timer);
> -	u8 mr_ifc_count;
> +	u32 mr_ifc_count;
>  
>  	igmpv3_send_cr(in_dev);
>  restart:
> -- 
> 2.32.0.605.g8dce9f2422-goog
>