linux-kernel - Re: [PATCH] rcu/performance: Fix kfree_perf_init() build warning on 32-bit kernels

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Message-ID: <20200527011413.GD149611@google.com>
Date:   Tue, 26 May 2020 21:14:13 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linux-tip-commits@...r.kernel.org, x86 <x86@...nel.org>
Subject: Re: [PATCH] rcu/performance: Fix kfree_perf_init() build warning on
 32-bit kernels

On Tue, May 26, 2020 at 08:27:44PM +0200, Ingo Molnar wrote:
[...]
> ./include/linux/kern_levels.h:5:18: warning: format ‘%lu’ expects argument
> of type ‘long unsigned int’, but argument 2 has type ‘unsigned int’
> [-Wformat=] 5 | #define KERN_SOH "\001"  /* ASCII Start Of Header */ |
> ^~~~~~
> ./include/linux/kern_levels.h:9:20: note: in expansion of macro ‘KERN_SOH’
>     9 | #define KERN_ALERT KERN_SOH "1" /* action must be taken immediately */
>       |                    ^~~~~~~~
> ./include/linux/printk.h:295:9: note: in expansion of macro ‘KERN_ALERT’
>   295 |  printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
>       |         ^~~~~~~~~~
> kernel/rcu/rcuperf.c:726:2: note: in expansion of macro ‘pr_alert’
>   726 |  pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj));
>       |  ^~~~~~~~
> kernel/rcu/rcuperf.c:726:32: note: format string is defined here
>   726 |  pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj));
>       |                              ~~^
>       |                                |
>       |                                long unsigned int
>       |                              %u
> 
> 
> The reason for the warning is that both kfree_mult and sizeof() are 
> 'int' types on 32-bit kernels, while the format string expects a long.
> 
> Instead of casting the type to long or tweaking the format string, the 
> most straightforward solution is to upgrade kfree_mult to a long. 
> Since this depends on CONFIG_RCU_PERF_TEST

Thanks for fixing it.

> BTW., could we please also rename this code from 'PERF_TEST'/'perf test'
> to 'PERFORMANCE_TEST'/'performance test'? At first glance I always
> mistakenly believe that it's somehow related to perf, while it isn't. =B-)

Would it be better to call it 'RCUPERF_TEST' instead of the
'RCU_PERFORMANCE_TEST' you are proposing? I feel the word 'PERFORMANCE' is
too long.  Also, 'rcuperf test' instead of the 'rcu performance test' you are
proposing.  I am Ok with doing it however you and Paul want it though, let me
know.

Paul, should I send you a renaming patch for the new performance tests as
well (which I believe should be in the -dev branch).

thanks,

 - Joel


> 
> Thanks,
> 
> 	Ingo
> 
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
>  kernel/rcu/rcuperf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
> index 16dd1e6b7c09..221a0a3810e4 100644
> --- a/kernel/rcu/rcuperf.c
> +++ b/kernel/rcu/rcuperf.c
> @@ -88,7 +88,7 @@ torture_param(bool, shutdown, RCUPERF_SHUTDOWN,
>  torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
>  torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
>  torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() perf test?");
> -torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate.");
> +torture_param(long, kfree_mult, 1, "Multiple of kfree_obj size to allocate.");
>  
>  static char *perf_type = "rcu";
>  module_param(perf_type, charp, 0444);