[PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

[PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The clalculation of fair_server_period_max includes an integer overflow:

In file included from kernel/sched/build_utility.c:72:
kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow]
  341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */

Avoids this by using an unsigned constant to start with.

Fixes: d741f297bcea ("sched/fair: Fair server interface")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 0148bc65d39c..242e7f264a0b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -338,7 +338,7 @@ enum dl_param {
 	DL_PERIOD,
 };
 
-static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
+static unsigned long fair_server_period_max = (1u << 22) * NSEC_PER_USEC; /* ~4 seconds */
 static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
 
 static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
-- 
2.39.2

Re: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

[Vincent Guittot]

Hi Arnd

On Wed, 7 Aug 2024 at 10:00, Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> The clalculation of fair_server_period_max includes an integer overflow:
>
> In file included from kernel/sched/build_utility.c:72:
> kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow]
>   341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
>
> Avoids this by using an unsigned constant to start with.

Dan sent something similar
https://lore.kernel.org/lkml/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain/

>
> Fixes: d741f297bcea ("sched/fair: Fair server interface")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 0148bc65d39c..242e7f264a0b 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -338,7 +338,7 @@ enum dl_param {
>         DL_PERIOD,
>  };
>
> -static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
> +static unsigned long fair_server_period_max = (1u << 22) * NSEC_PER_USEC; /* ~4 seconds */
>  static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
>
>  static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
> --
> 2.39.2
>

Re: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

[Peter Zijlstra]

On Wed, Aug 07, 2024 at 12:00:35PM +0200, Vincent Guittot wrote:
> Hi Arnd
> 
> On Wed, 7 Aug 2024 at 10:00, Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > The clalculation of fair_server_period_max includes an integer overflow:
> >
> > In file included from kernel/sched/build_utility.c:72:
> > kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow]
> >   341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
> >
> > Avoids this by using an unsigned constant to start with.
> 
> Dan sent something similar
> https://lore.kernel.org/lkml/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain/

Right, tglx also pointed me at a report for this. Let me go queue Dan's
patch.

> >
> > Fixes: d741f297bcea ("sched/fair: Fair server interface")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  kernel/sched/debug.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index 0148bc65d39c..242e7f264a0b 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -338,7 +338,7 @@ enum dl_param {
> >         DL_PERIOD,
> >  };
> >
> > -static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
> > +static unsigned long fair_server_period_max = (1u << 22) * NSEC_PER_USEC; /* ~4 seconds */
> >  static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
> >
> >  static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
> > --
> > 2.39.2
> >