On Wed, Jan 21, 2009 at 12:23:09PM +0000, David Howells (dhowells@xxxxxxxxxx) wrote:
> J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> > - Finally, we put_cred(override_creds(new)). That modifies
> > current->cred again, putting the old value and getting the
> > new.
> >
> > Hm. But that last part's not OK; aren't we still holding our own
> > reference to new, in addition to the one that override_creds() just
> > took? So I think we need the following?
>
> Yes, you're right. override_creds() takes an extra ref on the argument it is
> passed, thus leaving the caller with their original reference intact.
>
> So really, you don't want to call override_creds() as that will cost you an
> extra atomic_inc() and atomic_dec_and_test(). I recommend you replace:
>
> put_cred(override_creds(new));
>
> with:
>
> revert_creds(new);
>
> I think that should do the right thing. It may look a bit odd, but it'll be
> quicker. If you object to using revert_creds)( because of the name, we can
> come up with an alternative name.
With additional put_cred, i.e.:
put_cred(override_creds(new));
put_cred(new);
return 0;
I got following fun tcpdump and failed mount (it stuck, but can be interrupted):
15:34:41.253911 IP 77.88.20.183.1835336279 > 77.88.20.182.2049: 44 null
15:34:41.253916 IP 77.88.20.182.2049 > 77.88.20.183.728: . ack 44 win 88 <nop,nop,timestamp 125462 37402358>
15:34:41.254103 IP 77.88.20.182.2049 > 77.88.20.183.1835336279: reply ok 28 null
15:34:41.254229 IP 77.88.20.183.728 > 77.88.20.182.2049: . ack 29 win 89 <nop,nop,timestamp 37402358 125463>
15:34:41.254238 IP 77.88.20.183.1852113495 > 77.88.20.182.2049: 44 null
15:34:41.254271 IP 77.88.20.182.2049 > 77.88.20.183.1852113495: reply ok 28 null
15:34:41.254378 IP 77.88.20.183.1868890711 > 77.88.20.182.2049: 100 fsinfo [|nfs]
15:34:41.254411 IP 77.88.20.182.2049 > 77.88.20.183.1868890711: reply ok 36 fsinfo [|nfs]
15:34:41.254528 IP 77.88.20.183.1885667927 > 77.88.20.182.2049: 100 fsinfo [|nfs]
15:34:41.254555 IP 77.88.20.182.2049 > 77.88.20.183.1885667927: reply ok 36 fsinfo [|nfs]
But no corruption in the dmesg (like oops or bug).
--
Evgeniy Polyakov
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