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

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Date:   Tue, 26 May 2020 20:27:44 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-tip-commits@...r.kernel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Paul E. McKenney" <paulmck@...nel.org>, x86 <x86@...nel.org>
Subject: [PATCH] rcu/performance: Fix kfree_perf_init() build warning on
 32-bit kernels


* tip-bot2 for Joel Fernandes (Google) <tip-bot2@...utronix.de> wrote:

> The following commit has been merged into the core/rcu branch of tip:
> 
> Commit-ID:     f87dc808009ac86c790031627698ef1a34c31e25
> Gitweb:        https://git.kernel.org/tip/f87dc808009ac86c790031627698ef1a34c31e25
> Author:        Joel Fernandes (Google) <joel@...lfernandes.org>
> AuthorDate:    Mon, 16 Mar 2020 12:32:26 -04:00
> Committer:     Paul E. McKenney <paulmck@...nel.org>
> CommitterDate: Mon, 27 Apr 2020 11:02:50 -07:00
> 
> rcuperf: Add ability to increase object allocation size
> 
> This allows us to increase memory pressure dynamically using a new
> rcuperf boot command line parameter called 'rcumult'.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  kernel/rcu/rcuperf.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
> index a4a8d09..16dd1e6 100644
> --- a/kernel/rcu/rcuperf.c
> +++ b/kernel/rcu/rcuperf.c
> @@ -88,6 +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.");
>  
>  static char *perf_type = "rcu";
>  module_param(perf_type, charp, 0444);
> @@ -635,7 +636,7 @@ kfree_perf_thread(void *arg)
>  		}
>  
>  		for (i = 0; i < kfree_alloc_num; i++) {
> -			alloc_ptr = kmalloc(sizeof(struct kfree_obj), GFP_KERNEL);
> +			alloc_ptr = kmalloc(kfree_mult * sizeof(struct kfree_obj), GFP_KERNEL);
>  			if (!alloc_ptr)
>  				return -ENOMEM;
>  
> @@ -722,6 +723,8 @@ kfree_perf_init(void)
>  		schedule_timeout_uninterruptible(1);
>  	}
>  
> +	pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj));

There's a new build warning on certain 32-bit kernel builds due to 
this commit:

In file included from ./include/linux/printk.h:7,
                 from ./include/linux/kernel.h:15,
                 from kernel/rcu/rcuperf.c:13:
kernel/rcu/rcuperf.c: In function ‘kfree_perf_init’:
./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

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-)

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);