From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753428AbZK2OfV (ORCPT ); Sun, 29 Nov 2009 09:35:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752475AbZK2OfG (ORCPT ); Sun, 29 Nov 2009 09:35:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45862 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752179AbZK2OfF (ORCPT ); Sun, 29 Nov 2009 09:35:05 -0500 From: Avi Kivity To: Ingo Molnar , "H. Peter Anvin" Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH tip:x86/entry] core: fix user return notifier on fork() Date: Sun, 29 Nov 2009 16:34:48 +0200 Message-Id: <1259505288-16559-1-git-send-email-avi@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org fork() clones all thread_info flags, including TIF_USER_RETURN_NOTIFY; if the new task is first scheduled on a cpu which doesn't have user return notifiers set, this causes user return notifiers to trigger without any way of clearing itself. This is easy to trigger with a forky workload on the host in parallel with kvm, resulting in a cpu in an endless loop on the verge of returning to userspace. Fix by dropping the TIF_USER_RETURN_NOTIFY immediately after fork. Signed-off-by: Avi Kivity --- include/linux/user-return-notifier.h | 7 +++++++ kernel/fork.c | 2 ++ 2 files changed, 9 insertions(+), 0 deletions(-) diff --git a/include/linux/user-return-notifier.h b/include/linux/user-return-notifier.h index b6ac056..9c4a445 100644 --- a/include/linux/user-return-notifier.h +++ b/include/linux/user-return-notifier.h @@ -26,6 +26,11 @@ static inline void propagate_user_return_notify(struct task_struct *prev, void fire_user_return_notifiers(void); +static inline void clear_user_return_notifier(struct task_struct *p) +{ + clear_tsk_thread_flag(p, TIF_USER_RETURN_NOTIFY); +} + #else struct user_return_notifier {}; @@ -37,6 +42,8 @@ static inline void propagate_user_return_notify(struct task_struct *prev, static inline void fire_user_return_notifiers(void) {} +static inline void clear_user_return_notifier(struct task_struct *p) {} + #endif #endif diff --git a/kernel/fork.c b/kernel/fork.c index 166b8c4..7d4a348 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -64,6 +64,7 @@ #include #include #include +#include #include #include @@ -249,6 +250,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) goto out; setup_thread_stack(tsk, orig); + clear_user_return_notifier(tsk); stackend = end_of_stack(tsk); *stackend = STACK_END_MAGIC; /* for overflow detection */ -- 1.6.5.2