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Fix a LOR in the NFS client which could cause a deadlock.

Browse Source 
This was reported to the mailing list freebsd-net@freebsd.org
on July 21, 2011 under the subject "LOR with nfsclient sillyrename".
The LOR occurred when nfs_inactive() called vrele(sp->s_dvp)
while holding the vnode lock on the file in s_dvp. This patch
modifies the client so that it performs the vrele(sp->s_dvp)
as a separate task to avoid the LOR. This fix was discussed
with jhb@ and kib@, who both proposed variations of it.

Tested by:	pho, jlott at averesystems.com
Submitted by:	jhb (earlier version)
Reviewed by:	kib
Approved by:	re (kib)
MFC after:	2 weeks
This commit is contained in:
Rick Macklem 2011-08-02 11:24:42 +00:00
parent df6f430410
commit e498ea9037
2 changed files with 21 additions and 2 deletions
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21
sys/nfsclient/nfs_node.c
View File

@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
#include <sys/proc.h>
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <sys/taskqueue.h>
#include <sys/vnode.h>
#include <vm/uma.h>
@ -59,6 +60,8 @@ __FBSDID("$FreeBSD$");
static uma_zone_t nfsnode_zone;
static void nfs_freesillyrename(void *arg, __unused int pending);
#define TRUE 1
#define FALSE 0
@ -185,6 +188,20 @@ nfs_nget(struct mount *mntp, nfsfh_t *fhp, int fhsize, struct nfsnode **npp, int
return (0);
}
/*
* Do the vrele(sp->s_dvp) as a separate task in order to avoid a
* deadlock because of a LOR when vrele() locks the directory vnode.
*/
static void
nfs_freesillyrename(void *arg, __unused int pending)
{
struct sillyrename *sp;
sp = arg;
vrele(sp->s_dvp);
free(sp, M_NFSREQ);
}
int
nfs_inactive(struct vop_inactive_args *ap)
{
@ -207,8 +224,8 @@ nfs_inactive(struct vop_inactive_args *ap)
*/
(sp->s_removeit)(sp);
crfree(sp->s_cred);
vrele(sp->s_dvp);
free((caddr_t)sp, M_NFSREQ);
TASK_INIT(&sp->s_task, 0, nfs_freesillyrename, sp);
taskqueue_enqueue(taskqueue_thread, &sp->s_task);
mtx_lock(&np->n_mtx);
}
np->n_flag &= NMODIFIED;

2
sys/nfsclient/nfsnode.h
View File

@ -36,6 +36,7 @@
#ifndef _NFSCLIENT_NFSNODE_H_
#define _NFSCLIENT_NFSNODE_H_
#include <sys/_task.h>
#if !defined(_NFSCLIENT_NFS_H_) && !defined(_KERNEL)
#include <nfs/nfs.h>
#endif
@ -45,6 +46,7 @@
* can be removed by nfs_inactive()
*/
struct sillyrename {
struct task s_task;
struct ucred *s_cred;
struct vnode *s_dvp;
int (*s_removeit)(struct sillyrename *sp);