64 lines
2.2 KiB
Diff
64 lines
2.2 KiB
Diff
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# Commit ef55257bc81204e34691f1c2aa9e01f2d0768bdd
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# Date 2013-10-14 08:58:31 +0200
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# Author David Vrabel <david.vrabel@citrix.com>
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# Committer Jan Beulich <jbeulich@suse.com>
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sched: fix race between sched_move_domain() and vcpu_wake()
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From: David Vrabel <david.vrabel@citrix.com>
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sched_move_domain() changes v->processor for all the domain's VCPUs.
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If another domain, softirq etc. triggers a simultaneous call to
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vcpu_wake() (e.g., by setting an event channel as pending), then
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vcpu_wake() may lock one schedule lock and try to unlock another.
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vcpu_schedule_lock() attempts to handle this but only does so for the
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window between reading the schedule_lock from the per-CPU data and the
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spin_lock() call. This does not help with sched_move_domain()
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changing v->processor between the calls to vcpu_schedule_lock() and
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vcpu_schedule_unlock().
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Fix the race by taking the schedule_lock for v->processor in
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sched_move_domain().
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Signed-off-by: David Vrabel <david.vrabel@citrix.com>
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Acked-by: Juergen Gross <juergen.gross@ts.fujitsu.com>
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Use vcpu_schedule_lock_irq() (which now returns the lock) to properly
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retry the locking should the to be used lock have changed in the course
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of acquiring it (issue pointed out by George Dunlap).
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Add a comment explaining the state after the v->processor adjustment.
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Acked-by: Keir Fraser <keir@xen.org>
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--- a/xen/common/schedule.c
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+++ b/xen/common/schedule.c
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@@ -276,6 +276,8 @@ int sched_move_domain(struct domain *d,
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new_p = cpumask_first(c->cpu_valid);
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for_each_vcpu ( d, v )
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{
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+ spinlock_t *lock;
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+
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vcpudata = v->sched_priv;
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migrate_timer(&v->periodic_timer, new_p);
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@@ -283,7 +285,16 @@ int sched_move_domain(struct domain *d,
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migrate_timer(&v->poll_timer, new_p);
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cpumask_setall(v->cpu_affinity);
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+
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+ lock = vcpu_schedule_lock_irq(v);
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v->processor = new_p;
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+ /*
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+ * With v->processor modified we must not
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+ * - make any further changes assuming we hold the scheduler lock,
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+ * - use vcpu_schedule_unlock_irq().
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+ */
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+ spin_unlock_irq(lock);
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+
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v->sched_priv = vcpu_priv[v->vcpu_id];
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evtchn_move_pirqs(v);
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