svn commit: r197453 - in stable/7/sys: . contrib/pf kern
Attilio Rao
attilio at FreeBSD.org
Thu Sep 24 09:08:23 UTC 2009
Author: attilio
Date: Thu Sep 24 09:08:22 2009
New Revision: 197453
URL: http://svn.freebsd.org/changeset/base/197453
Log:
MFC r197223:
Fix a deadlock in sched_switch_migrate given by the runqueues being not
locked at once together when doing the switch.
Modified:
stable/7/sys/ (props changed)
stable/7/sys/contrib/pf/ (props changed)
stable/7/sys/kern/sched_ule.c
Modified: stable/7/sys/kern/sched_ule.c
==============================================================================
--- stable/7/sys/kern/sched_ule.c Thu Sep 24 08:35:17 2009 (r197452)
+++ stable/7/sys/kern/sched_ule.c Thu Sep 24 09:08:22 2009 (r197453)
@@ -1822,18 +1822,24 @@ sched_switch_migrate(struct tdq *tdq, st
*/
spinlock_enter();
thread_block_switch(td); /* This releases the lock on tdq. */
- TDQ_LOCK(tdn);
- tdq_add(tdn, td, flags);
- tdq_notify(td->td_sched);
- /*
- * After we unlock tdn the new cpu still can't switch into this
- * thread until we've unblocked it in cpu_switch(). The lock
- * pointers may match in the case of HTT cores. Don't unlock here
- * or we can deadlock when the other CPU runs the IPI handler.
+
+ /*
+ * Acquire both run-queue locks before placing the thread on the new
+ * run-queue to avoid deadlocks created by placing a thread with a
+ * blocked lock on the run-queue of a remote processor. The deadlock
+ * occurs when a third processor attempts to lock the two queues in
+ * question while the target processor is spinning with its own
+ * run-queue lock held while waiting for the blocked lock to clear.
*/
- if (TDQ_LOCKPTR(tdn) != TDQ_LOCKPTR(tdq)) {
- TDQ_UNLOCK(tdn);
+ if (TDQ_LOCKPTR(tdn) == TDQ_LOCKPTR(tdq)) {
TDQ_LOCK(tdq);
+ tdq_add(tdn, td, flags);
+ tdq_notify(td->td_sched);
+ } else {
+ tdq_lock_pair(tdn, tdq);
+ tdq_add(tdn, td, flags);
+ tdq_notify(td->td_sched);
+ TDQ_UNLOCK(tdn);
}
spinlock_exit();
#endif
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