On Tue, 23 Nov 2021 09:54:01 +0000 Ferruh Yigit <[email protected]> wrote:
> On 10/9/2021 3:03 AM, Stephen Hemminger wrote: > > On Sat, 9 Oct 2021 00:58:30 +0100 > > Ferruh Yigit <[email protected]> wrote: > > > >> To enable bifurcated device support, rtnl_lock is released before calling > >> userspace callbacks and asynchronous requests are enabled. > >> > >> But these changes caused more issues, like bug #809, #816. To reduce the > >> scope of the problems, the bifurcated device support related changes are > >> only enabled when it is requested explicitly with new 'enable_bifurcated' > >> module parameter. > >> And bifurcated device support is disabled by default. > >> > >> So the bifurcated device related problems are isolated and they can be > >> fixed without impacting all use cases. > >> > >> Bugzilla ID: 816 > >> Fixes: 631217c76135 ("kni: fix kernel deadlock with bifurcated device") > >> Cc: [email protected] > >> > >> Signed-off-by: Ferruh Yigit <[email protected]> > > > > Calling userspace with semaphore held is still risky and buggy. > > There is no guarantee that the userspace DPDK application will be well > > behaved. > > And if it is not, the spinning holding RTNL would break any other network > > management > > functions in the kernel. > > > > Hi Stephen, > > Because of what you described above, we tried the option that releases the > RTNL > lock before userspace callback, > That caused a deadlock in the ifdown, and we add a workaround for it. > > But now we are facing with two more issues because of the rtnl lock release, > - Bugzilla ID: 816, MAC set cause kernel deadlock > - Some requests are overwritten (because of the workaround we put for ifdown) > > This patch just converts the default behavior to what it was previously. > Releasing rtnl lock still supported with the module param, but I think it > is not good idea to make it default while it is know that it is buggy. > > @Thomas, @David, > Can it be possible to get this patch for -rc4? Since it has potential > to cause a deadlock in kernel as it is. > > I can send a new version with documentation update. Is it possible for userspace to choose the correct behavior instead of module option. Users will do it wrong. > > > These are the kind of problems that make me think it there should be a > > big "DO NOT USE THIS" onto KNI. Maybe make it print a big nasty message > > (see kernel VFIO without IOMMU description) or mark kernel as tainted?? > > > > See: https://fedoraproject.org/wiki/KernelStagingPolicy > > > > Something like: > > > > diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c > > index 611719b5ee27..d47fc6133cbe 100644 > > --- a/kernel/linux/kni/kni_net.c > > +++ b/kernel/linux/kni/kni_net.c > > @@ -838,6 +838,14 @@ kni_net_init(struct net_device *dev) > > dev->header_ops = &kni_net_header_ops; > > dev->ethtool_ops = &kni_net_ethtool_ops; > > dev->watchdog_timeo = WD_TIMEOUT; > > + > > + /* > > + * KNI is unsafe since it requires calling userspace to do > > + * control operations. And the overall quality according to > > + * kernel standards is the same as devices in staging. > > + */ > > + add_taint(TAINT_CRAP, LOCKDEP_STILL_OK); > > + netdev_warn(dev, "Adding kernel taint for KNI because it is not > > safe\n"); > > I am for discussing above separate from this patch, since this patch > restores the behavior that exist since KNI module exists. Any user of KNI will already get tainted because KNI is out of tree driver.
