Messages in this thread | | | Date | Thu, 24 May 2007 01:29:02 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset |
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Cliff Wickman wrote: > > In order to do this, move_task_off_dead_cpu() must make a call to > cpuset_cpus_allowed(), which may block. > > move_task_off_dead_cpu() has been within a critical region when called > from migrate_live_tasks(). So this patch also changes migrate_live_tasks() > to enable interrupts before calling move_task_off_dead_cpu(). > Since the tasklist_lock is dropped, the list scan must be restarted from > the top. > > [... snip ...] > > - * NOTE: interrupts should be disabled by the caller > + * NOTE: interrupts are not disabled by the caller > */ > static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) > { > @@ -5008,6 +5008,17 @@ restart: > if (dest_cpu == NR_CPUS) > dest_cpu = any_online_cpu(p->cpus_allowed); > > + /* try to stay on the same cpuset */ > + if (dest_cpu == NR_CPUS) { > + /* > + * Call to cpuset_cpus_allowed may sleep, so we depend > + * on move_task_off_dead_cpu() being called in a non-critical > + * region. > + */ > + p->cpus_allowed = cpuset_cpus_allowed(p); > + dest_cpu = any_online_cpu(p->cpus_allowed); > + }
I know nothing about cpuset.c, a _very_ naive question.
Do we really need task_lock() (used by cpuset_cpus_allowed) here ?
If not, probably we can make this simpler. CPU_DEAD takes cpuset_lock(), move_task_off_dead_cpu() uses guarantee_online_cpus() which doesn't sleep, so we don't need other changes.
Possible?
If not, this patch should also change migrate_dead(), it still calls move_task_off_dead_cpu() with irqs disabled, no?
Oleg.
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