From 8e7cac79808b62f242069a6ac88d364d35621371 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Sun, 29 Nov 2009 16:34:48 +0200 Subject: [PATCH] core: Fix user return notifier on fork() 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 LKML-Reference: <1259505288-16559-1-git-send-email-avi@redhat.com> Signed-off-by: Ingo Molnar --- include/linux/user-return-notifier.h | 7 +++++++ kernel/fork.c | 2 ++ 2 files changed, 9 insertions(+) diff --git a/include/linux/user-return-notifier.h b/include/linux/user-return-notifier.h index b6ac056291d7..9c4a445bb43c 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 266c6af6ef1b..1b7512d5a64a 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 */