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Date:	Mon, 16 May 2016 11:10:20 -0700
From:	Linus Torvalds <>
To:	Andy Lutomirski <>,
	Marcelo Tosatti <>,
	Paolo Bonzini <>
Cc:	"the arch/x86 maintainers" <>,
	Linux Kernel Mailing List <>
Subject: Re: Please review arch/x86/kernel/pvclock.c to fix Docker/Mono
 crashes in new Kernels

There is something odd being reported in Ubuntu.

There's a Mono SIGSEGV that was bisected to Andy's commit 1ddf0b1b11aa
("x86, vdso: Use asm volatile in __getcpu"), and then reported to be
fixed with commits

  80f7fdb1c7f0 ("x86: vdso: fix pvclock races with task migration")
  0a4e6be9ca17 ("x86: kvm: Revert "remove sched notifier for cross-cpu

and when those were backported all looked well.

But then those two commits in turn were reverted with

  73459e2a1ada ("x86: pvclock: Really remove the sched notifier for
cross-cpu migrations")

and people seem to report that it's back as a result:

so apparently that task migration notifier somehow does matter.



On Mon, May 16, 2016 at 1:13 AM,  <> wrote:
> Hello Linus,
> Am am sorry to bother you, but it seems that the bug from old kernels was
> copied to new >=4.1 kernels. We use Ubuntu/Docker/Mono and we had to
> rollback to 3.19.0-54 kernel for the work around.
> We found that a year ago there was a discussion on the launchpad
> ( regarding
> SIGSEGV on multi-cpu vm.
> It seems to me that the commits around that bug
> caused 4.1 and up kernels to keep that bug.
> Please review pvclock.c to fix that problem.
> Kiitos! Thank you!
> --
> Oleg Khalzov
> Vestbery

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