netdev - Re: [PATCH 1/2] workqueue: Have 'alloc_workqueue()' like macros accept a format specifier

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Date:   Mon, 19 Apr 2021 08:56:34 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>, tj@...nel.org,
        jiangshanlai@...il.com, saeedm@...dia.com, leon@...nel.org,
        davem@...emloft.net, kuba@...nel.org, bvanassche@....org
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] workqueue: Have 'alloc_workqueue()' like macros
 accept a format specifier

On 18/04/2021 23.26, Christophe JAILLET wrote:
> Improve 'create_workqueue', 'create_freezable_workqueue' and
> 'create_singlethread_workqueue' so that they accept a format
> specifier and a variable number of arguments.
> 
> This will put these macros more in line with 'alloc_ordered_workqueue' and
> the underlying 'alloc_workqueue()' function.
> 
> This will also allow further code simplification.
> 
> Suggested-by: Bart Van Assche <bvanassche@....org>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  include/linux/workqueue.h | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index d15a7730ee18..145e756ff315 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -425,13 +425,13 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
>  	alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED |		\
>  			__WQ_ORDERED_EXPLICIT | (flags), 1, ##args)
>  
> -#define create_workqueue(name)						\
> -	alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, 1, (name))
> +#define create_workqueue(fmt, args...)					\
> +	alloc_workqueue(fmt, __WQ_LEGACY | WQ_MEM_RECLAIM, 1, ##args)

The changes make sense, but are you sure that no current users of those
macros have some % character in the string they pass? If all users pass
string literals the compiler/0day bot should catch those, but as the
very example you give in 2/2 shows, not everybody passes string literals.

Maybe git grep would quickly tell that there's only 8 callers and they
are all audited quickly or something like that; in that case please
include a note to that effect in the commit log.

Rasmus