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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Paul,

On Tue, May 26, 2020 at 9:17 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> On Tue, May 26, 2020 at 08:27:44PM +0200, Ingo Molnar wrote:
> > * tip-bot2 for Joel Fernandes (Google) <tip-bot2@linutronix.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@joelfernandes.org>
> > > AuthorDate:    Mon, 16 Mar 2020 12:32:26 -04:00
> > > Committer:     Paul E. McKenney <paulmck@kernel.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@joelfernandes.org>
> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.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

> > > @@ -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

This issue is now upstream.

> > 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.

sizeof() is of type size_t, which is either unsigned int (32-bit) or
unsigned long (64-bit).
Hence the result of the multiplication is also of type size_t.

> >
> > 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

So the proper fix is Kefeng's patch from April:
"[PATCH -next] rcuperf: Fix printk format warning"
https://lore.kernel.org/r/20200417040245.66382-1-wangkefeng.wang@huawei.com

":"--
> Makes sense, and I have queued the patch below, which I am assuming
> that you want in the upcoming merge window.  If you don't tell me
> otherwise, I will send you an urgent pull request later today.
> Or, if you just put it directly into -tip yourself:
>
> Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
>
> Either way, please let me know.
>
> > 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-)
>
> Fair enough, especially given that perf was there first and is also way
> more heavily used.  ;-)
>
> But I am guessing that this one is OK for the v5.9 merge window.
> Either way, I will update as you say.
>
>                                                         Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 2fbc7d67a2ed108e3ac63296670fecb3a42fddd0
> Author: Ingo Molnar <mingo@kernel.org>
> Date:   Tue May 26 12:10:01 2020 -0700
>
>     rcuperf: Fix kfree_mult to match printk() format
>
>     This commit changes the type of kfree_mult from int to long in order
>     to match the printk() format on 32-bit systems.
>
>     Reported-by: kbuild test robot <lkp@intel.com>
>     Signed-off-by: Ingo Molnar <mingo@kernel.org>
>     Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
> index d906ca9..fb3a1f0 100644
> --- a/kernel/rcu/rcuperf.c
> +++ b/kernel/rcu/rcuperf.c
> @@ -93,7 +93,7 @@ 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);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds