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Document lock order and locking rules.

This commit is contained in:
riastradh 2017-10-25 06:02:40 +00:00
parent f697d47ee3
commit 2a7a645aaa
1 changed files with 22 additions and 3 deletions
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25
sys/kern/kern_event.c
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@ -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 offset */
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 */