On Sat, Jun 05, 2010 at 12:26:47PM -0700, Matthew Dillon wrote:
>
> :The vn structure appears to NOT be corrupt. Seems like a race if
> :vn->sc_cred goes from NULL to non-NULL between frame 6 and 5. Could
> :this be related to my recent link_elf change (setting p to proc0 if p
> :is NULL)?
> :
> :Joe
>
> Hmm. If devfs is racing access to that field then try changing the
> vnsetcred() code around a bit to this:
>
> struct ucred *ocred
> ...
>
>
> /*
> * Set credits in our softc
> */
> ocred = vn->sc_cred;
> vn->sc_cred = crdup(cred);
> if (ocred)
> crfree(ocred);
>
> If the race is more involved then that (assuming it is a race), we
> may have to call crhold() and friends whenever we use vn->sc_cred.
>
Sam,
Please try this patch. I was able to vnconfig a file following the
vkernel manpage without a panic. This isn't likely a long term
solution but will hopefully allow you to proceed with your GSoC work
in a vkernel. If you see this panic again let me know and I'll work
on implementing the crhold() et al. calls as Matt suggested.
Thanks,
Joe
diff --git a/sys/dev/disk/vn/vn.c b/sys/dev/disk/vn/vn.c
index 95bcf44..9f45281 100644
--- a/sys/dev/disk/vn/vn.c
+++ b/sys/dev/disk/vn/vn.c
@@ -697,7 +697,7 @@ vnsetcred(struct vn_softc *vn, struct ucred *cred)
* Set credits in our softc
*/
- if (vn->sc_cred)
+ if (vn->sc_cred && vn->sc_cred->cr_ref > 0)
crfree(vn->sc_cred);
vn->sc_cred = crdup(cred);
