* [PATCH] cpuset: restore sanity to cpuset_cpus_allowed_fallback()
@ 2019-03-07 0:54 Joel Savitz
2019-03-07 14:42 ` Joel Savitz
0 siblings, 1 reply; 3+ messages in thread
From: Joel Savitz @ 2019-03-07 0:54 UTC (permalink / raw)
To: linux-kernel; +Cc: Joel Savitz, Li Zefan, cgroups
If a process is limited by taskset (i.e. cpuset) to only be allowed to
run on cpu N, and then cpu N is offlined via hotplug, the process will
be assigned the current value of its cpuset cgroup's effective_cpus field
in a call to do_set_cpus_allowed() in cpuset_cpus_allowed_fallback().
This argument's value does not makes sense for this case, because
task_cs(tsk)->effective_cpus is modified by cpuset_hotplug_workfn()
to reflect the new value of cpu_active_mask after cpu N is removed from
the mask. While this may make sense for the cgroup affinity mask, it
does not make sense on a per-task basis, as a task that was previously
limited to only be run on cpu N will be limited to every cpu _except_ for
cpu N after it is offlined/onlined via hotplug.
Pre-patch behavior:
$ grep Cpus /proc/$$/status
Cpus_allowed: ff
Cpus_allowed_list: 0-7
$ taskset -p 4 $$
pid 19202's current affinity mask: f
pid 19202's new affinity mask: 4
$ grep Cpus /proc/self/status
Cpus_allowed: 04
Cpus_allowed_list: 2
# echo off > /sys/devices/system/cpu/cpu2/online
$ grep Cpus /proc/$$/status
Cpus_allowed: 0b
Cpus_allowed_list: 0-1,3
# echo on > /sys/devices/system/cpu/cpu2/online
$ grep Cpus /proc/$$/status
Cpus_allowed: 0b
Cpus_allowed_list: 0-1,3
On a patched system, the final grep produces the following
output instead:
$ grep Cpus /proc/$$/status
Cpus_allowed: ff
Cpus_allowed_list: 0-7
This patch changes the above behavior by instead simply resetting the mask
to cpu_possible_mask.
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
---
kernel/cgroup/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 479743db6c37..5f65a2167bdf 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3243,7 +3243,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
rcu_read_lock();
- do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
+ do_set_cpus_allowed(tsk, cpu_possible_mask);
rcu_read_unlock();
/*
--
2.20.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] cpuset: restore sanity to cpuset_cpus_allowed_fallback()
2019-03-07 0:54 [PATCH] cpuset: restore sanity to cpuset_cpus_allowed_fallback() Joel Savitz
@ 2019-03-07 14:42 ` Joel Savitz
[not found] ` <CAL1p7m7n7+wwHsrxywnUYpOKvT6N+5ewCjaZXLPLCsBk+t+oNw@mail.gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: Joel Savitz @ 2019-03-07 14:42 UTC (permalink / raw)
To: linux-kernel; +Cc: Li Zefan, cgroups, Philip Auld
On Wed, Mar 6, 2019 at 7:55 PM Joel Savitz <jsavitz@redhat.com> wrote:
>
> If a process is limited by taskset (i.e. cpuset) to only be allowed to
> run on cpu N, and then cpu N is offlined via hotplug, the process will
> be assigned the current value of its cpuset cgroup's effective_cpus field
> in a call to do_set_cpus_allowed() in cpuset_cpus_allowed_fallback().
> This argument's value does not makes sense for this case, because
> task_cs(tsk)->effective_cpus is modified by cpuset_hotplug_workfn()
> to reflect the new value of cpu_active_mask after cpu N is removed from
> the mask. While this may make sense for the cgroup affinity mask, it
> does not make sense on a per-task basis, as a task that was previously
> limited to only be run on cpu N will be limited to every cpu _except_ for
> cpu N after it is offlined/onlined via hotplug.
>
> Pre-patch behavior:
>
> $ grep Cpus /proc/$$/status
> Cpus_allowed: ff
> Cpus_allowed_list: 0-7
>
> $ taskset -p 4 $$
> pid 19202's current affinity mask: f
> pid 19202's new affinity mask: 4
>
> $ grep Cpus /proc/self/status
> Cpus_allowed: 04
> Cpus_allowed_list: 2
>
> # echo off > /sys/devices/system/cpu/cpu2/online
> $ grep Cpus /proc/$$/status
> Cpus_allowed: 0b
> Cpus_allowed_list: 0-1,3
>
> # echo on > /sys/devices/system/cpu/cpu2/online
> $ grep Cpus /proc/$$/status
> Cpus_allowed: 0b
> Cpus_allowed_list: 0-1,3
>
> On a patched system, the final grep produces the following
> output instead:
>
> $ grep Cpus /proc/$$/status
> Cpus_allowed: ff
> Cpus_allowed_list: 0-7
>
> This patch changes the above behavior by instead simply resetting the mask
> to cpu_possible_mask.
>
> Signed-off-by: Joel Savitz <jsavitz@redhat.com>
> ---
> kernel/cgroup/cpuset.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 479743db6c37..5f65a2167bdf 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3243,7 +3243,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
> void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
> {
> rcu_read_lock();
> - do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
> + do_set_cpus_allowed(tsk, cpu_possible_mask);
> rcu_read_unlock();
>
> /*
> --
> 2.20.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-03-26 17:32 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2019-03-07 0:54 [PATCH] cpuset: restore sanity to cpuset_cpus_allowed_fallback() Joel Savitz
2019-03-07 14:42 ` Joel Savitz
[not found] ` <CAL1p7m7n7+wwHsrxywnUYpOKvT6N+5ewCjaZXLPLCsBk+t+oNw@mail.gmail.com>
2019-03-26 17:32 ` Joel Savitz
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox