x86/smpboot: Initialize secondary CPU only if master CPU will wait for it
authorIgor Mammedov <imammedo@redhat.com>
Fri, 20 Jun 2014 12:23:11 +0000 (14:23 +0200)
committerIngo Molnar <mingo@kernel.org>
Tue, 16 Sep 2014 09:11:32 +0000 (11:11 +0200)
commitce4b1b16502b182368cda20a61de2995762c8bcc
tree0980e8e7cabc1489114e757ac311dda9986a745c
parent9e82bf014195d6f0054982c463575cdce24292be
x86/smpboot: Initialize secondary CPU only if master CPU will wait for it

Hang is observed on virtual machines during CPU hotplug,
especially in big guests with many CPUs. (It reproducible
more often if host is over-committed).

It happens because master CPU gives up waiting on
secondary CPU and allows it to run wild. As result
AP causes locking or crashing system. For example
as described here:

  https://lkml.org/lkml/2014/3/6/257

If master CPU have sent STARTUP IPI successfully,
and AP signalled to master CPU that it's ready
to start initialization, make master CPU wait
indefinitely till AP is onlined.

To ensure that AP won't ever run wild, make it
wait at early startup till master CPU confirms its
intention to wait for AP. If AP doesn't respond in 10
seconds, the master CPU will timeout and cancel
AP onlining.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1403266991-12233-1-git-send-email-imammedo@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/cpu/common.c
arch/x86/kernel/smpboot.c
arch/x86/xen/smp.c