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- lookup_once: when crossing a mount point, don't keep the parent vnode locked.

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ie. don't lock a vnode while holding another vnode which belongs to a
  different filesystem.  otherwise we propagate slowness (or deadness) of a
  filesystem to another via vnode lock chain.
- lookup_parsepath: don't alter vnode states.  let the caller do it instead.
- add comments and assertions.
This commit is contained in:
yamt 2010-12-17 22:34:04 +00:00
parent ef99b60b5d
commit 1ad15d6549
1 changed files with 35 additions and 10 deletions
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45
sys/kern/vfs_lookup.c
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@ -1,4 +1,4 @@
/* $NetBSD: vfs_lookup.c,v 1.125 2010/11/30 10:43:05 dholland Exp $ */
/* $NetBSD: vfs_lookup.c,v 1.126 2010/12/17 22:34:04 yamt Exp $ */
/*
* Copyright (c) 1982, 1986, 1989, 1993
@ -37,7 +37,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.125 2010/11/30 10:43:05 dholland Exp $");
__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.126 2010/12/17 22:34:04 yamt Exp $");
#include "opt_magiclinks.h"
@ -696,6 +696,7 @@ do_namei(struct namei_state *state)
}
return error;
}
KASSERT(VOP_ISLOCKED(state->namei_startdir) == LK_EXCLUSIVE);
/* Loop through symbolic links */
for (;;) {
@ -904,6 +905,11 @@ lookup_start(struct namei_state *state)
return 0;
}
/*
* lookup_parsepath: consume a component name from state->ndp and prepare
* state->cnp for it.
*/
static int
lookup_parsepath(struct namei_state *state)
{
@ -922,16 +928,12 @@ lookup_parsepath(struct namei_state *state)
* cnp->cn_nameptr for callers that need the name. Callers needing
* the name set the SAVENAME flag. When done, they assume
* responsibility for freeing the pathname buffer.
*
* At this point, our only vnode state is that "dp" is held and locked.
*/
cnp->cn_consume = 0;
cp = NULL;
cnp->cn_hash = namei_hash(cnp->cn_nameptr, &cp);
cnp->cn_namelen = cp - cnp->cn_nameptr;
if (cnp->cn_namelen > NAME_MAX) {
vput(state->dp);
ndp->ni_dvp = NULL;
return ENAMETOOLONG;
}
#ifdef NAMEI_DIAGNOSTIC
@ -982,6 +984,21 @@ lookup_parsepath(struct namei_state *state)
return 0;
}
/*
* lookup_once: look up the vnode for the next component name (state->cnp).
*
* takes care of dot-dot, cross-mount, and MNT_UNION.
*
* inputs:
* state->dp the parent vnode
* state->cnp the componentname to lookup
*
* outputs:
* state->dp the result vnode
* ndp->ni_vp updated to state->dp
* ndp->ni_dvp updated to the parent directory vnode
*/
static int
lookup_once(struct namei_state *state)
{
@ -1136,6 +1153,8 @@ unionlookup:
* "state->dp" and "ndp->ni_dvp" are both locked and held,
* and may be the same vnode.
*/
KASSERT(VOP_ISLOCKED(state->dp) == LK_EXCLUSIVE);
KASSERT(VOP_ISLOCKED(ndp->ni_dvp) == LK_EXCLUSIVE);
/*
* Check to see if the vnode has been mounted on;
@ -1157,10 +1176,9 @@ unionlookup:
vn_lock(ndp->ni_dvp, LK_EXCLUSIVE | LK_RETRY);
return error;
}
VOP_UNLOCK(tdp);
ndp->ni_vp = state->dp = tdp;
vn_lock(ndp->ni_dvp, LK_EXCLUSIVE | LK_RETRY);
vn_lock(ndp->ni_vp, LK_EXCLUSIVE | LK_RETRY);
vrele(ndp->ni_dvp);
vref(tdp);
ndp->ni_dvp = ndp->ni_vp = state->dp = tdp;
}
return 0;
@ -1187,8 +1205,14 @@ do_lookup(struct namei_state *state)
}
dirloop:
/*
* At this point, our only vnode state is that "dp" is held and locked.
*/
KASSERT(VOP_ISLOCKED(state->dp) == LK_EXCLUSIVE);
KASSERT(ndp->ni_dvp == NULL);
error = lookup_parsepath(state);
if (error) {
vput(state->dp);
goto bad;
}
@ -1235,6 +1259,7 @@ dirloop:
} else {
vput(ndp->ni_dvp);
}
ndp->ni_dvp = NULL;
goto dirloop;
}