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Fix PR7373 for real: Rearrange locking to avoid need for LOCKPARENT in lookup

This commit is contained in:
sommerfeld 1999-06-21 05:11:09 +00:00
parent f337a5c974
commit c45e268d01
1 changed files with 94 additions and 55 deletions
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149
sys/kern/vfs_getcwd.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vfs_getcwd.c,v 1.7 1999/06/19 18:01:26 sommerfeld Exp $ */
/* $NetBSD: vfs_getcwd.c,v 1.8 1999/06/21 05:11:09 sommerfeld Exp $ */
/*-
* Copyright (c) 1999 The NetBSD Foundation, Inc.
@ -54,7 +54,7 @@
#include <sys/syscallargs.h>
static int
getcwd_scandir __P((struct vnode *, struct vnode **,
getcwd_scandir __P((struct vnode **, struct vnode **,
char **, char *, struct proc *));
static int
getcwd_getcache __P((struct vnode **, struct vnode **,
@ -79,10 +79,13 @@ int vn_isunder __P((struct vnode *, struct vnode *, struct proc *));
*
* Place the name in the buffer which starts at bufp, immediately
* before *bpp, and move bpp backwards to point at the start of it.
*
* On entry, *cvpp is a locked vnode reference; on exit, it is vput and NULL'ed
* On exit, *pvpp is either NULL or is a locked vnode reference.
*/
static int
getcwd_scandir(cvp, pvpp, bpp, bufp, p)
struct vnode *cvp;
getcwd_scandir(cvpp, pvpp, bpp, bufp, p)
struct vnode **cvpp;
struct vnode **pvpp;
char **bpp;
char *bufp;
@ -99,16 +102,31 @@ getcwd_scandir(cvp, pvpp, bpp, bufp, p)
ino_t fileno;
struct vattr va;
struct vnode *pvp = NULL;
struct vnode *cvp = *cvpp;
struct componentname cn;
int len, reclen;
tries = 0;
/*
* If we want the filename, get some info we need while the
* current directory is still locked.
*/
if (bufp != NULL) {
error = VOP_GETATTR(cvp, &va, p->p_ucred, p);
if (error) {
vput(cvp);
*cvpp = NULL;
*pvpp = NULL;
return error;
}
}
/*
* Ok, we have to do it the hard way..
* First, get parent vnode using lookup of ..
* Next, get parent vnode using lookup of ..
*/
cn.cn_nameiop = LOOKUP;
cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY | LOCKPARENT;
cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
cn.cn_proc = p;
cn.cn_cred = p->p_ucred;
cn.cn_pnbuf = NULL;
@ -116,28 +134,28 @@ getcwd_scandir(cvp, pvpp, bpp, bufp, p)
cn.cn_namelen = 2;
cn.cn_hash = 0;
cn.cn_consume = 0;
/*
* At this point, cvp is locked, and will be locked
* on return in all cases.
* On successful return, *pvpp will also be locked
* At this point, cvp is locked and will be unlocked by the lookup.
* On successful return, *pvpp will be locked
*/
error = VOP_LOOKUP(cvp, pvpp, &cn);
if (error) {
vput(cvp);
*cvpp = NULL;
*pvpp = NULL;
return error;
}
pvp = *pvpp;
/* If we don't care about the pathname, we're done */
if (bufp == NULL)
if (bufp == NULL) {
vrele(cvp);
*cvpp = NULL;
return 0;
}
error = VOP_GETATTR(cvp, &va, p->p_ucred, p);
if (error)
return error;
fileno = va.va_fileid;
dirbuflen = DIRBLKSIZ;
if (dirbuflen < va.va_blocksize)
@ -163,14 +181,8 @@ unionread:
eofflag = 0;
/* XXX un-break adosfs */
VOP_UNLOCK(cvp, 0);
error = VOP_READDIR(pvp, &uio, p->p_ucred, &eofflag, 0, 0);
/* XXX not handling lock failures here.. */
(void) vn_lock(cvp, LK_EXCLUSIVE | LK_RETRY);
off = uio.uio_offset;
/*
@ -250,6 +262,8 @@ unionread:
error = ENOENT;
out:
vrele(cvp);
*cvpp = NULL;
free(dirbuf, M_TEMP);
return error;
}
@ -258,7 +272,14 @@ out:
* Look in the vnode-to-name reverse cache to see if
* we can find things the easy way.
*
* XXX vn_lock/vget failure paths are untested.
* XXX vget failure path is untested.
*
* On entry, *vpp is a locked vnode reference.
* On exit, one of the following is the case:
* 0) Both *vpp and *vpp are NULL and failure is returned.
* 1) *dvpp is NULL, *vpp remains locked and -1 is returned (cache miss)
* 2) *dvpp is a locked vnode reference, *vpp is vput and NULL'ed
* and 0 is returned (cache hit)
*/
static int
@ -269,39 +290,52 @@ getcwd_getcache(vpp, dvpp, bpp, bufp)
{
struct vnode *cvp, *pvp = NULL;
int error;
int vpid;
cvp = *vpp;
error = cache_revlookup(cvp, dvpp, bpp, bufp);
if (error)
return error;
pvp = *dvpp;
/*
* Do a little dance with the locks to avoid deadlocking
* someone going the other way. Since we're going up, we have
* to release the current lock before we take the parent lock,
* and then re-take the current lock. Since either lock can
* fail, causing us to abort, this is a little convoluted.
* This returns 0 on a cache hit, -1 on a clean cache miss,
* or an errno on other failure.
*/
error = cache_revlookup(cvp, dvpp, bpp, bufp);
if (error) {
if (error != -1) {
vput(cvp);
*vpp = NULL;
*dvpp = NULL;
}
return error;
}
pvp = *dvpp;
vpid = pvp->v_id;
/*
* Since we're going up, we have to release the current lock
* before we take the parent lock.
*/
VOP_UNLOCK(cvp, 0);
/* cur now unlocked... */
error = vget(pvp, LK_EXCLUSIVE | LK_RETRY);
if (error != 0) {
vrele(cvp);
*vpp = NULL;
if (error != 0)
*dvpp = NULL;
return error;
/*
* Check that vnode capability didn't change while we were waiting
* for the lock.
*/
if (error || (vpid != pvp->v_id)) {
/*
* oops, it did. do this the hard way.
*/
if (!error) vput(pvp);
error = vn_lock(cvp, LK_EXCLUSIVE | LK_RETRY);
*dvpp = NULL;
return -1;
}
/* parent is now locked */
error = vn_lock(cvp, LK_EXCLUSIVE | LK_RETRY);
if (error != 0) {
vrele(cvp);
*vpp = NULL;
return error;
}
/* ok, cur is now locked again.. */
vrele(cvp);
*vpp = NULL;
return 0;
}
@ -356,8 +390,8 @@ static int getcwd_common (dvp, rvp, bpp, bufp, limit, flags, p)
* - we run out of space in the buffer.
*/
if (dvp == rvp) {
if (bufp)
*(--(*bpp)) = '/';
if (bp)
*(--bp) = '/';
goto out;
}
do {
@ -407,28 +441,28 @@ static int getcwd_common (dvp, rvp, bpp, bufp, limit, flags, p)
* Look in the name cache; if that fails, look in the
* directory..
*/
error = getcwd_getcache(&dvp, &pvp, bpp, bufp);
error = getcwd_getcache(&dvp, &pvp, &bp, bufp);
if (error == -1)
error = getcwd_scandir(dvp, &pvp, bpp, bufp, p);
error = getcwd_scandir(&dvp, &pvp, &bp, bufp, p);
if (error)
goto out;
#if DIAGNOSTIC
if (dvp == pvp) {
panic("getcwd: oops, dvp == pvp");
}
if (dvp != NULL)
panic("getcwd: oops, forgot to null dvp");
if (bufp && (bp <= bufp)) {
panic("getcwd: oops, went back too far");
}
#endif
if (bufp) *(--(*bpp)) = '/';
vput(dvp);
if (bp)
*(--bp) = '/';
dvp = pvp;
pvp = NULL;
limit--;
} while ((dvp != rvp) && (limit > 0));
out:
if (bpp)
*bpp = bp;
if (pvp)
vput(pvp);
if (dvp)
@ -510,6 +544,11 @@ int sys___getcwd(p, v, retval)
bend = bp;
*(--bp) = '\0';
/*
* 5th argument here is "max number of vnodes to traverse".
* Since each entry takes up at least 2 bytes in the output buffer,
* limit it to N/2 vnodes for an N byte buffer.
*/
error = getcwd_common (p->p_cwdi->cwdi_cdir, NULL, &bp, path, len/2,
GETCWD_CHECK_ACCESS, p);