From: Ingo Molnar <mingo@elte.hu>
- remove the hotplug lock from around much of fork(), and re-copy the
cpus_allowed mask to solve the hotplug race cleanly.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/kernel/fork.c | 22 +++++++++++-----------
25-akpm/kernel/sched.c | 14 +-------------
2 files changed, 12 insertions(+), 24 deletions(-)
diff -puN kernel/fork.c~sched-fork-hotplug-cleanuppatch kernel/fork.c
--- 25/kernel/fork.c~sched-fork-hotplug-cleanuppatch 2004-07-28 22:08:44.798220624 -0700
+++ 25-akpm/kernel/fork.c 2004-07-28 22:08:44.805219560 -0700
@@ -892,16 +892,6 @@ struct task_struct *copy_process(unsigne
if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
return ERR_PTR(-EINVAL);
- /*
- * The newly dup'ed task shares the same cpus_allowed mask as its
- * parent (ie. current), and it is not attached to the tasklist.
- * The end result is that this CPU might go down and the parent
- * be migrated away, leaving the task on a dead CPU. So take the
- * hotplug lock here and release it after the child has been attached
- * to the tasklist.
- */
- lock_cpu_hotplug();
-
retval = security_task_create(clone_flags);
if (retval)
goto fork_out;
@@ -1042,6 +1032,17 @@ struct task_struct *copy_process(unsigne
/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);
+
+ /*
+ * The task hasn't been attached yet, so cpus_allowed mask cannot
+ * have changed. The cpus_allowed mask of the parent may have
+ * changed after it was copied first time, and it may then move to
+ * another CPU - so we re-copy it here and set the child's CPU to
+ * the parent's CPU. This avoids alot of nasty races.
+ */
+ p->cpus_allowed = current->cpus_allowed;
+ set_task_cpu(p, smp_processor_id());
+
/*
* Check for pending SIGKILL! The new thread should not be allowed
* to slip out of an OOM kill. (or normal SIGKILL.)
@@ -1107,7 +1108,6 @@ struct task_struct *copy_process(unsigne
retval = 0;
fork_out:
- unlock_cpu_hotplug();
if (retval)
return ERR_PTR(retval);
return p;
diff -puN kernel/sched.c~sched-fork-hotplug-cleanuppatch kernel/sched.c
--- 25/kernel/sched.c~sched-fork-hotplug-cleanuppatch 2004-07-28 22:08:44.801220168 -0700
+++ 25-akpm/kernel/sched.c 2004-07-28 22:08:44.808219104 -0700
@@ -873,22 +873,10 @@ static int find_idlest_cpu(struct task_s
/*
* Perform scheduler related setup for a newly forked process p.
- * p is forked by current. The cpu hotplug lock is held.
+ * p is forked by current.
*/
void fastcall sched_fork(task_t *p)
{
- int cpu = smp_processor_id();
-
- /*
- * The task hasn't been attached yet, so cpus_allowed mask cannot
- * change. The cpus_allowed mask of the parent may have changed
- * after it is copied, and it may then move to a CPU that is not
- * allowed for the child.
- */
- if (unlikely(!cpu_isset(cpu, p->cpus_allowed)))
- cpu = any_online_cpu(p->cpus_allowed);
- set_task_cpu(p, cpu);
-
/*
* We mark the process as running here, but have not actually
* inserted it onto the runqueue yet. This guarantees that
_