path: root/kernel
diff options
authorPaolo Bonzini <pbonzini@redhat.com>2015-04-23 13:20:18 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2015-04-27 15:49:30 +0200
commit73459e2a1ada09a68c02cc5b73f3116fc8194b3d (patch)
tree2d85beb72d2ee970926f65554099764e2cdc1f9c /kernel
parent5dca0d9147458be9b9363b8a484aa77d710b412a (diff)
x86: pvclock: Really remove the sched notifier for cross-cpu migrations
This reverts commits 0a4e6be9ca17c54817cf814b4b5aa60478c6df27 and 80f7fdb1c7f0f9266421f823964fd1962681f6ce. The task migration notifier was originally introduced in order to support the pvclock vsyscall with non-synchronized TSC, but KVM only supports it with synchronized TSC. Hence, on KVM the race condition is only needed due to a bad implementation on the host side, and even then it's so rare that it's mostly theoretical. As far as KVM is concerned it's possible to fix the host, avoiding the additional complexity in the vDSO and the (re)introduction of the task migration notifier. Xen, on the other hand, hasn't yet implemented vsyscall support at all, so we do not care about its plans for non-synchronized TSC. Reported-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'kernel')
1 files changed, 0 insertions, 15 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9123a82cbb6..fe22f7510bce 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1016,13 +1016,6 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
rq_clock_skip_update(rq, true);
-static ATOMIC_NOTIFIER_HEAD(task_migration_notifier);
-void register_task_migration_notifier(struct notifier_block *n)
- atomic_notifier_chain_register(&task_migration_notifier, n);
void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
@@ -1053,18 +1046,10 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
trace_sched_migrate_task(p, new_cpu);
if (task_cpu(p) != new_cpu) {
- struct task_migration_notifier tmn;
if (p->sched_class->migrate_task_rq)
p->sched_class->migrate_task_rq(p, new_cpu);
perf_sw_event_sched(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 0);
- tmn.task = p;
- tmn.from_cpu = task_cpu(p);
- tmn.to_cpu = new_cpu;
- atomic_notifier_call_chain(&task_migration_notifier, 0, &tmn);
__set_task_cpu(p, new_cpu);

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