linux-kernel - Re: [PATCH 1/1] u64_stats: fix u64_stats_init() for lockdep when used repeatedly in one file

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Date: Mon, 11 Mar 2024 18:25:16 +0100
From: Petr Tesařík <petr@...arici.cz>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Linux regressions mailing list
 <regressions@...ts.linux.dev>, linux-kernel@...r.kernel.org (open list)
Cc: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@...mhuis.info>, stable@...nel.org
Subject: Re: [PATCH 1/1] u64_stats: fix u64_stats_init() for lockdep when
 used repeatedly in one file

On Wed,  6 Mar 2024 12:11:57 +0100
Petr Tesarik <petr@...arici.cz> wrote:

> Fix bogus lockdep warnings if multiple u64_stats_sync variables are
> initialized in the same file.
> 
> With CONFIG_LOCKDEP, seqcount_init() is a macro which declares:
> 
> 	static struct lock_class_key __key;
> 
> Since u64_stats_init() is a function (albeit an inline one), all calls
> within the same file end up using the same instance, effectively treating
> them all as a single lock-class.

What happens with this fix now?

IIUC it should be reviewed by Eric, but I don't know through which tree
it should be merged. Any plans yet?

Petr T

> Cc: stable@...nel.org
> Fixes: 9464ca650008 ("net: make u64_stats_init() a function")
> Closes: https://lore.kernel.org/netdev/ea1567d9-ce66-45e6-8168-ac40a47d1821@roeck-us.net/
> Signed-off-by: Petr Tesarik <petr@...arici.cz>
> ---
>  include/linux/u64_stats_sync.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
> index ffe48e69b3f3..457879938fc1 100644
> --- a/include/linux/u64_stats_sync.h
> +++ b/include/linux/u64_stats_sync.h
> @@ -135,10 +135,11 @@ static inline void u64_stats_inc(u64_stats_t *p)
>  	p->v++;
>  }
>  
> -static inline void u64_stats_init(struct u64_stats_sync *syncp)
> -{
> -	seqcount_init(&syncp->seq);
> -}
> +#define u64_stats_init(syncp)				\
> +	do {						\
> +		struct u64_stats_sync *__s = (syncp);	\
> +		seqcount_init(&__s->seq);		\
> +	} while (0)
>  
>  static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp)
>  {