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cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus()

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Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use
get_online_cpus and put_online_cpus instead as it highlights the
refcount semantics in these operations.

The new API guarantees protection against the cpu-hotplug operation, but
it doesn't guarantee serialized access to any of the local data
structures. Hence the changes needs to be reviewed.

In case of pseries_add_processor/pseries_remove_processor, use
cpu_maps_update_begin()/cpu_maps_update_done() as we're modifying the
cpu_present_map there.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Gautham R Shenoy
2008-01-25 21:08:02 +01:00
committed by Ingo Molnar
parent d221938c04
commit 86ef5c9a8e
15 changed files with 62 additions and 61 deletions
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14
kernel/cpuset.c
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@@ -537,10 +537,10 @@ static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
*
* Call with cgroup_mutex held. May take callback_mutex during
* call due to the kfifo_alloc() and kmalloc() calls. May nest
* a call to the lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
* a call to the get_online_cpus()/put_online_cpus() pair.
* Must not be called holding callback_mutex, because we must not
* call lock_cpu_hotplug() while holding callback_mutex. Elsewhere
* the kernel nests callback_mutex inside lock_cpu_hotplug() calls.
* call get_online_cpus() while holding callback_mutex. Elsewhere
* the kernel nests callback_mutex inside get_online_cpus() calls.
* So the reverse nesting would risk an ABBA deadlock.
*
* The three key local variables below are:
@@ -691,9 +691,9 @@ restart:
rebuild:
/* Have scheduler rebuild sched domains */
lock_cpu_hotplug();
get_online_cpus();
partition_sched_domains(ndoms, doms);
unlock_cpu_hotplug();
put_online_cpus();
done:
if (q && !IS_ERR(q))
@@ -1617,10 +1617,10 @@ static struct cgroup_subsys_state *cpuset_create(
*
* If the cpuset being removed has its flag 'sched_load_balance'
* enabled, then simulate turning sched_load_balance off, which
* will call rebuild_sched_domains(). The lock_cpu_hotplug()
* will call rebuild_sched_domains(). The get_online_cpus()
* call in rebuild_sched_domains() must not be made while holding
* callback_mutex. Elsewhere the kernel nests callback_mutex inside
* lock_cpu_hotplug() calls. So the reverse nesting would risk an
* get_online_cpus() calls. So the reverse nesting would risk an
* ABBA deadlock.
*/