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authorPaul Jackson <pj@sgi.com>2005-05-20 13:59:15 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-05-20 15:48:19 -0700
commitb39c4fab259b216148e705344a892c96efe1946d (patch)
parentb2665f92ae67a2d086537979d317a6f3a5697c63 (diff)
[PATCH] cpusets+hotplug+preepmt broken
This patch removes the entwining of cpusets and hotplug code in the "No more Mr. Nice Guy" case of sched.c move_task_off_dead_cpu(). Since the hotplug code is holding a spinlock at this point, we cannot take the cpuset semaphore, cpuset_sem, as would seem to be required either to update the tasks cpuset, or to scan up the nested cpuset chain, looking for the nearest cpuset ancestor that still has some CPUs that are online. So we just punt and blast the tasks cpus_allowed with all bits allowed. This reverts these lines of code to what they were before the cpuset patch. And it updates the cpuset Doc file, to match. The one known alternative to this that seems to work came from Dinakar Guniguntala, and required the hotplug code to take the cpuset_sem semaphore much earlier in its processing. So far as we know, the increased locking entanglement between cpusets and hot plug of this alternative approach is not worth doing in this case. Signed-off-by: Paul Jackson <pj@sgi.com> Acked-by: Nathan Lynch <ntl@pobox.com> Acked-by: Dinakar Guniguntala <dino@in.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2 files changed, 2 insertions, 3 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 1ad26d2c20ae..2f8f24eaefd9 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -252,8 +252,7 @@ in a tasks processor placement.
There is an exception to the above. If hotplug funtionality is used
to remove all the CPUs that are currently assigned to a cpuset,
then the kernel will automatically update the cpus_allowed of all
-tasks attached to CPUs in that cpuset with the online CPUs of the
-nearest parent cpuset that still has some CPUs online. When memory
+tasks attached to CPUs in that cpuset to allow all CPUs. When memory
hotplug functionality for removing Memory Nodes is available, a
similar exception is expected to apply there as well. In general,
the kernel prefers to violate cpuset placement, over starving a task
diff --git a/kernel/sched.c b/kernel/sched.c
index 0dc3158667a2..66b2ed784822 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4243,7 +4243,7 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
/* No more Mr. Nice Guy. */
if (dest_cpu == NR_CPUS) {
- tsk->cpus_allowed = cpuset_cpus_allowed(tsk);
+ cpus_setall(tsk->cpus_allowed);
dest_cpu = any_online_cpu(tsk->cpus_allowed);