Date: Fri, 16 Apr 2010 13:23:17 -0700 From: "Matthew Fleming" <matthew.fleming@isilon.com> To: <freebsd-stable@freebsd.org> Subject: panic in vget() Message-ID: <06D5F9F6F655AD4C92E28B662F7F853E039387EF@seaxch09.desktop.isilon.com>
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I'm looking at this panic in vget() on stable/7:
if (vp->v_iflag & VI_DOOMED && (flags & LK_RETRY) =3D=3D 0)
panic("vget: vn_lock failed to return ENOENT\n");
It seems to me that this is not a correct assertion, because if the
caller passed in no lock flags (i.e. just checking the vnode for
validity) then there is a window between the VI_UNLOCK() in _vn_lock(9)
and the subsequent VI_LOCK() in vget() where another thread could have
set VI_DOOMED.
This isn't a problem on CURRENT because the code has been changed to not
allow an empty lock flags.
I believe the following is a potential fix is:
vholdl(vp);
if ((error =3D vn_lock(vp, flags | LK_INTERLOCK, td)) !=3D 0) {
vdrop(vp);
return (error);
}
VI_LOCK(vp);
+ /*
+ * Deal with a timing window when the interlock is not held
+ * and VI_DOOMED can be set, since we only have a holdcnt,
+ * not a usecount.
+ */
+ if (vp->v_iflag & VI_DOOMED && (flags & LK_RETRY) =3D=3D 0) {
+ KASSERT((flags & LK_TYPE_MASK) =3D=3D 0, ("Unexpected flags
%x", flags));
+ vdropl(vp);
+ return (ENOENT);
+ }
/* Upgrade our holdcnt to a usecount. */
v_upgrade_usecount(vp);
- if (vp->v_iflag & VI_DOOMED && (flags & LK_RETRY) =3D=3D 0)
- panic("vget: vn_lock failed to return ENOENT\n");
if (oweinact) {
if (vp->v_iflag & VI_OWEINACT)
vinactive(vp, td);
VI_UNLOCK(vp);
if ((oldflags & LK_TYPE_MASK) =3D=3D 0)
Thanks,
matthew
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