Introduce safe memory reclamation, a mechanism for reclaiming shared

objects that readers can access without locking. This provides a basis
for read-copy-update operations.

Readers access SMR-protected shared objects inside SMR read-side
critical section where sleeping is not allowed. To reclaim
an SMR-protected object, the writer has to ensure mutual exclusion of
other writers, remove the object's shared reference and wait until
read-side references cannot exist any longer. As an alternative to
waiting, the writer can schedule a callback that gets invoked when
reclamation is safe.

The mechanism relies on CPU quiescent states to determine when an
SMR-protected object is ready for reclamation.

The <sys/smr.h> header additionally provides an implementation of
singly- and doubly-linked lists that can be used together with SMR.
These lists allow lockless read access with a concurrent writer.

Discussed with many
OK mpi@ sashan@

1 files changed, 4 insertions, 1 deletions

diff --git a/sys/kern/sched_bsd.c b/sys/kern/sched_bsd.c
index 635f10664a5..00a08861b59 100644
--- a/sys/kern/sched_bsd.c
+++ b/sys/kern/sched_bsd.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sched_bsd.c,v 1.49 2019/01/28 11:48:13 mpi Exp $	*/
+/*	$OpenBSD: sched_bsd.c,v 1.50 2019/02/26 14:24:21 visa Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*-
@@ -47,6 +47,7 @@
 #include <uvm/uvm_extern.h>
 #include <sys/sched.h>
 #include <sys/timeout.h>
+#include <sys/smr.h>
 
 #ifdef KTRACE
 #include <sys/ktrace.h>
@@ -417,6 +418,8 @@ mi_switch(void)
 
 	SCHED_ASSERT_UNLOCKED();
 
+	smr_idle();
+
 	/*
 	 * We're running again; record our new start time.  We might
 	 * be running on a new CPU now, so don't use the cache'd