diff options
| -rw-r--r-- | sys/kern/sched_ule.c | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c index 27e8371dff2b..fd14fc4021a3 100644 --- a/sys/kern/sched_ule.c +++ b/sys/kern/sched_ule.c @@ -1749,19 +1749,19 @@ sched_switch_migrate(struct tdq *tdq, struct thread *td, int flags) */ spinlock_enter(); thread_block_switch(td); /* This releases the lock on tdq. */ - TDQ_LOCK(tdn); - tdq_add(tdn, td, flags); - tdq_notify(tdn, td); + /* - * 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); - TDQ_LOCK(tdq); - } + tdq_lock_pair(tdn, tdq); + tdq_add(tdn, td, flags); + tdq_notify(tdn, td); + TDQ_UNLOCK(tdn); spinlock_exit(); #endif return (TDQ_LOCKPTR(tdn)); |