From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>,
Konrad Wilk <konrad.wilk@oracle.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Mukesh Ojha <mojha@codeaurora.org>,
Peter Zijlstra <peterz@infradead.org>,
Jiri Kosina <jkosina@suse.cz>, Rik van Riel <riel@surriel.com>,
Andy Lutomirski <luto@kernel.org>,
Micheal Kelley <michael.h.kelley@microsoft.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Greg KH <gregkh@linuxfoundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>,
x86@kernel.org
Subject: [patch 0/2] cpu/hotplug: Prevent damage with SMP=y and HOTPLUG_CPU=n
Date: Tue, 26 Mar 2019 17:36:04 +0100 [thread overview]
Message-ID: <20190326163604.348882514@linutronix.de> (raw)
Tianyu reported a crash with SMP=y and HOTPLUG_CPU=n plus 'nosmt' on the
kernel command line.
https://lkml.kernel.org/r/1553521883-20868-1-git-send-email-Tianyu.Lan@microsoft.com
The reason is a bug in the hotplug code which does not handle the fact,
that HOTPLUG_CPU=n cannot tear down a CPU completely.
Unfortunately HOTPLUG_CPU cannot be enforced as some architectures do not
support it at all.
The fix is only a workaround because a full solution is not possible due to
the limitations of HOTPLUG_CPU=n. So the CPU stays around in an undead state.
As 'nosmt' has become popular recently, the proper solution for X86 is to
enforce HOTPLUG_CPU when SMP is enabled.
Thanks,
tglx
----
arch/x86/Kconfig | 8 +-------
kernel/cpu.c | 20 ++++++++++++++++++--
2 files changed, 19 insertions(+), 9 deletions(-)
next reply other threads:[~2019-03-26 16:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-26 16:36 Thomas Gleixner [this message]
2019-03-26 16:36 ` [patch 1/2] cpu/hotplug: Prevent crash when CPU bringup fails on CONFIG_HOTPLUG_CPU=n Thomas Gleixner
2019-03-27 1:12 ` Greg KH
2019-03-28 12:38 ` [tip:smp/urgent] " tip-bot for Thomas Gleixner
2019-03-26 16:36 ` [patch 2/2] x86/smp: Enforce CONFIG_HOTPLUG_CPU when SMP=y Thomas Gleixner
2019-03-27 1:12 ` Greg KH
2019-03-28 12:39 ` [tip:smp/urgent] " tip-bot for Thomas Gleixner
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