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PR kern/38141 lookup/vfs_busy acquire rwlock recursively 

Until the code paths are fixed properly, put in place an ugly workaround
to make it safe to recursively acquire a read lock on a mount.
This commit is contained in:
ad 2008-05-02 17:40:30 +00:00
parent 62c4a64698
commit 04feebca3b
2 changed files with 23 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
sys/kern/vfs_subr.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vfs_subr.c,v 1.339 2008/04/30 12:49:16 ad Exp $ */
/* $NetBSD: vfs_subr.c,v 1.340 2008/05/02 17:40:30 ad Exp $ */
/*-
* Copyright (c) 1997, 1998, 2004, 2005, 2007, 2008 The NetBSD Foundation, Inc.
@ -75,7 +75,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.339 2008/04/30 12:49:16 ad Exp $");
__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.340 2008/05/02 17:40:30 ad Exp $");
#include "opt_ddb.h"
#include "opt_compat_netbsd.h"
@ -285,6 +285,7 @@ try_nextlist:
static inline int
vfs_dobusy(struct mount *mp, const krw_t op, struct mount **nextp)
{
lwp_t *l;
KASSERT(mp->mnt_refcnt > 0);
@ -292,14 +293,17 @@ vfs_dobusy(struct mount *mp, const krw_t op, struct mount **nextp)
if (nextp != NULL) {
mutex_exit(&mountlist_lock);
}
if (mp->mnt_writer == curlwp) {
mp->mnt_recursecnt++;
l = curlwp;
if (l->l_mpbusy == mp) {
if (op == RW_WRITER) {
KASSERT(rw_write_held(&mp->mnt_lock));
} else {
KASSERT(rw_lock_held(&mp->mnt_lock));
}
l->l_mprecurse++;
} else {
rw_enter(&mp->mnt_lock, op);
if (op == RW_WRITER) {
KASSERT(mp->mnt_writer == NULL);
mp->mnt_writer = curlwp;
}
l->l_mpbusy = mp;
}
if (__predict_false((mp->mnt_iflag & IMNT_GONE) != 0)) {
if (nextp != NULL) {
@ -399,15 +403,18 @@ vfs_trybusy(struct mount *mp, krw_t op, struct mount **nextp)
void
vfs_unbusy(struct mount *mp, bool keepref, struct mount **nextp)
{
lwp_t *l;
KASSERT(mp->mnt_refcnt > 0);
if (mp->mnt_writer == curlwp) {
KASSERT(rw_write_held(&mp->mnt_lock));
if (mp->mnt_recursecnt != 0) {
mp->mnt_recursecnt--;
l = curlwp;
if (l->l_mpbusy != NULL) {
KASSERT(l->l_mpbusy == mp);
KASSERT(rw_lock_held(&mp->mnt_lock));
if (l->l_mprecurse != 0) {
l->l_mprecurse--;
} else {
mp->mnt_writer = NULL;
l->l_mpbusy = NULL;
rw_exit(&mp->mnt_lock);
}
} else {

4
sys/sys/lwp.h
View File

@ -1,4 +1,4 @@
/* $NetBSD: lwp.h,v 1.92 2008/04/29 13:02:03 ad Exp $ */
/* $NetBSD: lwp.h,v 1.93 2008/05/02 17:40:30 ad Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@ -165,6 +165,8 @@ struct lwp {
uint64_t l_pfailtime; /* !: for kernel preemption */
uintptr_t l_pfailaddr; /* !: for kernel preemption */
uintptr_t l_pfaillock; /* !: for kernel preemption */
void *l_mpbusy; /* !: XXX hack for vfs_busy */
int l_mprecurse; /* !: XXX hack for vfs_busy */
/* These are only used by 'options SYSCALL_TIMES' */
uint32_t l_syscall_time; /* !: time epoch for current syscall */