* Zhao Chenhui | 2013-06-09 17:59:42 [+0800]:
>No. _cpu_down() on mainline do not change the cpus_allowed.
My bad.
>The problem is that the task which turned off cpu2 (for instance)
>can not run on cpu2 again after cpu2 is turned on, because cpu2 has been
>removed from the cpus_allowed of the task.
>
>The task can put himself back on cpu2 throuhg the system call,
>but I think applications should not do this work and do not care which cpu
>it is running on in most time.
The mask needs to be changed because you may not be on the CPU while it
is going down. What do you think about:
Subject: [PATCH] kernel/hotplug: restore original cpu mask oncpu/down
If a task which is allowed to run only on CPU X puts CPU Y down then it
will be allowed on all CPUs but the on CPU Y after it comes back from
kernel. This patch ensures that we don't lose the initial setting unless
the CPU the task is running is going down.
Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
kernel/cpu.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 3acf17d..f5ad8e1 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -545,6 +545,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
.hcpu = hcpu,
};
cpumask_var_t cpumask;
+ cpumask_var_t cpumask_org;
if (num_online_cpus() == 1)
return -EBUSY;
@@ -555,6 +556,12 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
/* Move the downtaker off the unplug cpu */
if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
return -ENOMEM;
+ if (!alloc_cpumask_var(&cpumask_org, GFP_KERNEL)) {
+ free_cpumask_var(cpumask);
+ return -ENOMEM;
+ }
+
+ cpumask_copy(cpumask_org, tsk_cpus_allowed(current));
cpumask_andnot(cpumask, cpu_online_mask, cpumask_of(cpu));
set_cpus_allowed_ptr(current, cpumask);
free_cpumask_var(cpumask);
@@ -563,7 +570,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
if (mycpu == cpu) {
printk(KERN_ERR "Yuck! Still on unplug CPU\n!");
migrate_enable();
- return -EBUSY;
+ err = -EBUSY;
+ goto restore_cpus;
}
cpu_hotplug_begin();
@@ -622,6 +630,9 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
cpu_hotplug_done();
if (!err)
cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
+restore_cpus:
+ set_cpus_allowed_ptr(current, cpumask_org);
+ free_cpumask_var(cpumask_org);
return err;
}
--
1.7.10.4
>
>-Chenhui
Sebastian
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
