Module Name: src
Committed By: riastradh
Date: Wed Oct 25 06:02:40 UTC 2017
Modified Files:
src/sys/kern: kern_event.c
Log Message:
Document lock order and locking rules.
To generate a diff of this commit:
cvs rdiff -u -r1.94 -r1.95 src/sys/kern/kern_event.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_event.c
diff -u src/sys/kern/kern_event.c:1.94 src/sys/kern/kern_event.c:1.95
--- src/sys/kern/kern_event.c:1.94 Sat Sep 16 23:55:16 2017
+++ src/sys/kern/kern_event.c Wed Oct 25 06:02:40 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_event.c,v 1.94 2017/09/16 23:55:16 christos Exp $ */
+/* $NetBSD: kern_event.c,v 1.95 2017/10/25 06:02:40 riastradh Exp $ */
/*-
* Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -58,7 +58,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_event.c,v 1.94 2017/09/16 23:55:16 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_event.c,v 1.95 2017/10/25 06:02:40 riastradh Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -170,7 +170,26 @@ static int user_kfilterc; /* current o
static int user_kfiltermaxc; /* max size so far */
static size_t user_kfiltersz; /* size of allocated memory */
-/* Locks */
+/*
+ * Global Locks.
+ *
+ * Lock order:
+ *
+ * kqueue_filter_lock
+ * -> kn_kq->kq_fdp->fd_lock
+ * -> object lock (e.g., device driver lock, kqueue_misc_lock, &c.)
+ * -> kn_kq->kq_lock
+ *
+ * Locking rules:
+ *
+ * f_attach: fdp->fd_lock, KERNEL_LOCK
+ * f_detach: fdp->fd_lock, KERNEL_LOCK
+ * f_event(!NOTE_SUBMIT) via kevent: fdp->fd_lock, _no_ object lock
+ * f_event via knote: whatever caller guarantees
+ * Typically, f_event(NOTE_SUBMIT) via knote: object lock
+ * f_event(!NOTE_SUBMIT) via knote: nothing,
+ * acquires/releases object lock inside.
+ */
static krwlock_t kqueue_filter_lock; /* lock on filter lists */
static kmutex_t kqueue_misc_lock; /* miscellaneous */
