[CentOS-virt] Xen 4.6.6-9 (with XPTI meltdown mitigation) packages making their way to centos-virt-xen-testing

Pasi Kärkkäinen pasik at iki.fi
Fri May 4 19:11:41 UTC 2018


On Wed, Jan 24, 2018 at 09:30:33AM -0800, Nathan March wrote:
> 
> > -----Original Message-----
> > From: CentOS-virt [mailto:centos-virt-bounces at centos.org] On Behalf Of
> > Johnny Hughes
> > Sent: Wednesday, January 24, 2018 6:39 AM
> > To: centos-virt at centos.org
> > Subject: Re: [CentOS-virt] Xen 4.6.6-9 (with XPTI meltdown mitigation)
> > packages making their way to centos-virt-xen-testing
> > 
> > On 01/24/2018 01:01 AM, Pasi Kärkkäinen wrote:
> > > On Tue, Jan 23, 2018 at 06:20:39PM -0600, Kevin Stange wrote:
> > >> On 01/23/2018 05:57 PM, Karl Johnson wrote:
> > >>>
> > >>>
> > >>> On Tue, Jan 23, 2018 at 4:50 PM, Nathan March <nathan at gt.net
> > >>> <mailto:nathan at gt.net>> wrote:
> > >>>
> > >>>     Hi,
> > >>>
> > >>>     > Hmm.. isn't this the ldisc bug that was discussed a few months ago
> > on this
> > >>>     list,
> > >>>     > and a patch was applied to virt-sig kernel aswell?
> > >>>     >
> > >>>     > Call trace looks similar..
> > >>>
> > >>>     Good memory! I'd forgotten about that despite being the one who ran
> > >>>     into it.
> > >>>
> > >>>     Looks like that patch was just removed in 4.9.75-30 which I just
> > >>>     upgraded
> > >>>     this system to: http://cbs.centos.org/koji/buildinfo?buildID=21122
> > >>>     <http://cbs.centos.org/koji/buildinfo?buildID=21122>
> > >>>     Previously I was on 4.9.63-29 which does not have this problem, and
> > does
> > >>>     have the ldisc patch. So I guess the question is for Johnny, why was it
> > >>>     removed?
> > >>>
> > >>>     In the meantime, I'll revert the kernel and follow up if I see any
> > >>>     further
> > >>>     problems.
> > >>>
> > >>>
> > >>> IIRC the patch has been removed from the spec file because it has been
> > >>> merged upstream in 4.9.71.
> > >>
> > >> The IRC discussion I found in my log indicates that it was removed
> > >> because it didn't apply cleanly due to changes when updating to 4.9.75,
> > >> yet I don't think anyone independently validated that the changes made
> > >> are equivalent to the patch that was removed.  I was never able to
> > >> reproduce this issue, so I didn't investigate it myself.
> > >>
> > >
> > > Sounds like the patch is still needed :)
> > >
> > > Anyone up to re-porting it to 4.9.75+ ?
> > 
> > It looked, at first glance, like 4.9.71 fixed it .. I guess not in all cases
> 
> I'm happy to do testing here if anyone's able to help with a patch, does look like reverting to 4.9.63-29 solved it for me in the interm.
> 

Hello Nathan,

I noticed Upstream Linux now has some patches related to tty_ldisc .. as you seem to have an easily reproducible way of triggering the crashes, could you please try if these patches fix the issue, when applied to CentOS 4.9 kernel?


"tty: fix data race between tty_init_dev and flush of buf":
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/tty_ldisc.c?id=b027e2298bd588d6fa36ed2eda97447fb3eac078

"tty: Avoid possible error pointer dereference at tty_ldisc_restore().":
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/tty_ldisc.c?id=598c2d41ff44889dd8eced4f117403e472158d85

"tty: Don't call panic() at tty_ldisc_init()":
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/tty_ldisc.c?id=903f9db10f18f735e62ba447147b6c434b6af003

"tty: Use __GFP_NOFAIL for tty_ldisc_get()":
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/tty_ldisc.c?id=bcdd0ca8cb8730573afebcaae4138f8f4c8eaa20


Thanks,

-- Pasi



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