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- Solve a race where we could lose a call to VOP_INACTIVE. If vget() waiting

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on a lock held the last usecount ref on a vnode and the lock failed we
   would not call INACTIVE.  Solve this by only holding a holdcnt to prevent
   the vnode from disappearing while we wait on vn_lock.  Other callers
   may now VOP_INACTIVE while we are waiting on the lock, however this race
   is acceptable, while losing INACTIVE is not.

Discussed with:	kan, pjd
Tested by:	kkenn
Sponsored by:	Isilon Systems, Inc.
MFC After:	1 week
This commit is contained in:
jeff 2006-02-01 00:30:05 +00:00
parent 30a231055b
commit 47857ecfe1
1 changed files with 30 additions and 12 deletions
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42
sys/kern/vfs_subr.c
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@ -95,6 +95,7 @@ static void vinactive(struct vnode *, struct thread *);
static void v_incr_usecount(struct vnode *);
static void v_decr_usecount(struct vnode *);
static void v_decr_useonly(struct vnode *);
static void v_upgrade_usecount(struct vnode *);
static void vfree(struct vnode *);
static void vnlru_free(int);
static void vdestroy(struct vnode *);
@ -1861,6 +1862,24 @@ v_incr_usecount(struct vnode *vp)
vholdl(vp);
}
/*
* Turn a holdcnt into a use+holdcnt such that only one call to
* v_decr_usecount is needed.
*/
static void
v_upgrade_usecount(struct vnode *vp)
{
CTR3(KTR_VFS, "v_upgrade_usecount: vp %p holdcnt %d usecount %d\n",
vp, vp->v_holdcnt, vp->v_usecount);
vp->v_usecount++;
if (vp->v_type == VCHR && vp->v_rdev != NULL) {
dev_lock();
vp->v_rdev->si_usecount++;
dev_unlock();
}
}
/*
* Decrement the vnode use and hold count along with the driver's usecount
* if this is a chardev. The vdropl() below releases the vnode interlock
@ -1916,7 +1935,7 @@ v_decr_useonly(struct vnode *vp)
* been changed to a new filesystem type).
*/
int
vget( struct vnode *vp, int flags, struct thread *td)
vget(struct vnode *vp, int flags, struct thread *td)
{
int oweinact;
int oldflags;
@ -1925,6 +1944,7 @@ vget( struct vnode *vp, int flags, struct thread *td)
error = 0;
oldflags = flags;
oweinact = 0;
VFS_ASSERT_GIANT(vp->v_mount);
if ((flags & LK_INTERLOCK) == 0)
VI_LOCK(vp);
/*
@ -1941,28 +1961,24 @@ vget( struct vnode *vp, int flags, struct thread *td)
flags |= LK_EXCLUSIVE;
oweinact = 1;
}
v_incr_usecount(vp);
vholdl(vp);
if ((error = vn_lock(vp, flags | LK_INTERLOCK, td)) != 0) {
VI_LOCK(vp);
/*
* must expand vrele here because we do not want
* to call VOP_INACTIVE if the reference count
* drops back to zero since it was never really
* active.
*/
v_decr_usecount(vp);
vdrop(vp);
return (error);
}
VI_LOCK(vp);
/* Upgrade our holdcnt to a usecount. */
v_upgrade_usecount(vp);
if (vp->v_iflag & VI_DOOMED && (flags & LK_RETRY) == 0)
panic("vget: vn_lock failed to return ENOENT\n");
if (oweinact) {
VI_LOCK(vp);
if (vp->v_iflag & VI_OWEINACT)
vinactive(vp, td);
VI_UNLOCK(vp);
if ((oldflags & LK_TYPE_MASK) == 0)
VOP_UNLOCK(vp, 0, td);
}
} else
VI_UNLOCK(vp);
return (0);
}
@ -2010,6 +2026,7 @@ vrele(struct vnode *vp)
struct thread *td = curthread; /* XXX */
KASSERT(vp != NULL, ("vrele: null vp"));
VFS_ASSERT_GIANT(vp->v_mount);
VI_LOCK(vp);
@ -2061,6 +2078,7 @@ vput(struct vnode *vp)
KASSERT(vp != NULL, ("vput: null vp"));
ASSERT_VOP_LOCKED(vp, "vput");
VFS_ASSERT_GIANT(vp->v_mount);
VI_LOCK(vp);
/* Skip this v_writecount check if we're going to panic below. */
VNASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1, vp,