Author: mjg
Date: Tue Jul 28 07:05:49 2020
New Revision: 363634
URL: https://svnweb.freebsd.org/changeset/base/363634
Log:
MFC r363511:
Do a lockless check in kthread_suspend_check
Modified:
stable/12/sys/kern/kern_kthread.c
Directory Properties:
stable/12/ (props changed)
Modified: stable/12/sys/kern/kern_kthread.c
==============================================================================
--- stable/12/sys/kern/kern_kthread.c Tue Jul 28 07:04:46 2020
(r363633)
+++ stable/12/sys/kern/kern_kthread.c Tue Jul 28 07:05:49 2020
(r363634)
@@ -444,12 +444,15 @@ kthread_suspend_check(void)
panic("%s: curthread is not a valid kthread", __func__);
/*
- * As long as the double-lock protection is used when accessing the
- * TDF_KTH_SUSP flag, synchronizing the read operation via proc mutex
- * is fine.
+ * Setting the TDF_KTH_SUSP flag is protected by process lock.
+ *
+ * Do an unlocked read first to avoid serializing with all other threads
+ * in the common case of not suspending.
*/
+ if ((td->td_flags & TDF_KTH_SUSP) == 0)
+ return;
PROC_LOCK(p);
- while (td->td_flags & TDF_KTH_SUSP) {
+ while ((td->td_flags & TDF_KTH_SUSP) != 0) {
wakeup(&td->td_flags);
msleep(&td->td_flags, &p->p_mtx, PPAUSE, "ktsusp", 0);
}
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