Received-SPF: pass (google.com: domain of linux-kernel+bounces-64903-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Wed, 14 Feb 2024 10:01:27 +0100
From: Borislav Petkov <bp@alien8.de>
To: Costa Shulyupin <costa.shul@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
	Waiman Long <longman@redhat.com>,
	Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH v2] hrtimer: select housekeeping CPU during migration
Message-ID: <20240214090127.GAZcyBZ9mRTrSOoCSR@fat_crate.local>
References: <20240211135213.2518068-1-costa.shul@redhat.com>
 <20240213164650.2935909-3-costa.shul@redhat.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20240213164650.2935909-3-costa.shul@redhat.com>
Content-Transfer-Encoding: quoted-printable

On Tue, Feb 13, 2024 at 06:46:51PM +0200, Costa Shulyupin wrote:
> During CPU-down hotplug, hrtimers may migrate to isolated CPUs,
> compromising CPU isolation. This commit addresses this issue by
> masking valid CPUs for hrtimers using housekeeping_cpumask(HK_TYPE_TIME=
R).
>=20
> Suggested-by: Waiman Long <longman@redhat.com>
> Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
> Reviewed-by: Waiman Long <longman@redhat.com>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>=20
> Changes in v2:
> - [v1] https://lore.kernel.org/all/20240211135213.2518068-1-costa.shul@=
redhat.com/
> - reworded and rebased on linux-next
> ---
>  kernel/time/hrtimer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index edb0f821dcea..947bd6cf7105 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -2224,7 +2224,7 @@ static void migrate_hrtimer_list(struct hrtimer_c=
lock_base *old_base,
>  int hrtimers_cpu_dying(unsigned int dying_cpu)
>  {
>  	struct hrtimer_cpu_base *old_base, *new_base;
> -	int i, ncpu =3D cpumask_first(cpu_active_mask);
> +	int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekeeping(HK_TYPE=
_TIMER));
							^^^^^^^^^^^^^^
How was this patch tested?

It even says housekeeping_cpumask() in the commit message so the
*intent* to use the correct function is there:

kernel/time/hrtimer.c: In function =E2=80=98hrtimers_cpu_dying=E2=80=99:
kernel/time/hrtimer.c:2226:56: error: implicit declaration of function =E2=
=80=98housekeeping=E2=80=99 [-Werror=3Dimplicit-function-declaration]
 2226 |         int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekee=
ping(HK_TYPE_TIMER));
      |                                                        ^~~~~~~~~~=
~~
/include/linux/cpumask.h:774:67: note: in definition of macro =E2=80=98c=
pumask_any_and=E2=80=99
  774 | #define cpumask_any_and(mask1, mask2) cpumask_first_and((mask1), =
(mask2))
      |                                                                  =
 ^~~~~
kernel/time/hrtimer.c:2226:69: error: =E2=80=98HK_TYPE_TIMER=E2=80=99 und=
eclared (first use in this function)
 2226 |         int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekee=
ping(HK_TYPE_TIMER));
      |                                                                  =
   ^~~~~~~~~~~~~
/include/linux/cpumask.h:774:67: note: in definition of macro =E2=80=98c=
pumask_any_and=E2=80=99
  774 | #define cpumask_any_and(mask1, mask2) cpumask_first_and((mask1), =
(mask2))
      |                                                                  =
 ^~~~~
kernel/time/hrtimer.c:2226:69: note: each undeclared identifier is report=
ed only once for each function it appears in
 2226 |         int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekee=
ping(HK_TYPE_TIMER));
      |                                                                  =
   ^~~~~~~~~~~~~
/include/linux/cpumask.h:774:67: note: in definition of macro =E2=80=98c=
pumask_any_and=E2=80=99
  774 | #define cpumask_any_and(mask1, mask2) cpumask_first_and((mask1), =
(mask2))
      |                                                                  =
 ^~~~~
cc1: some warnings being treated as errors
make[4]: *** [scripts/Makefile.build:243: kernel/time/hrtimer.o] Error 1
make[3]: *** [scripts/Makefile.build:481: kernel/time] Error 2
make[2]: *** [scripts/Makefile.build:481: kernel] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/mnt/kernel/kernel/2nd/linux/Makefile:1921: .] Error 2
make: *** [Makefile:240: __sub-make] Error 2

This makes it build again at least:

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 2cbdf64d746c..6057fe2e179b 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -38,6 +38,7 @@
 #include <linux/sched/deadline.h>
 #include <linux/sched/nohz.h>
 #include <linux/sched/debug.h>
+#include <linux/sched/isolation.h>
 #include <linux/timer.h>
 #include <linux/freezer.h>
 #include <linux/compat.h>
@@ -2223,7 +2224,7 @@ static void migrate_hrtimer_list(struct hrtimer_clo=
ck_base *old_base,
=20
 int hrtimers_cpu_dying(unsigned int dying_cpu)
 {
-	int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekeeping(HK_TYPE_T=
IMER));
+	int i, ncpu =3D cpumask_any_and(cpu_active_mask, housekeeping_cpumask(H=
K_TYPE_TIMER));
 	struct hrtimer_cpu_base *old_base, *new_base;
=20
 	tick_cancel_sched_timer(dying_cpu);


--=20
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette