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authorOleg Nesterov <oleg@redhat.com>2014-10-05 16:23:22 -0400
committerIngo Molnar <mingo@kernel.org>2014-10-28 05:46:05 -0400
commit009f60e2763568cdcd75bd1cf360c7c7165e2e60 (patch)
tree190e6cb5857bd0c2788939fe4004a128e655ec49
parent6419265899d9bd27e5ff9f8b43db3715407fc2ba (diff)
sched: stop the unbound recursion in preempt_schedule_context()
preempt_schedule_context() does preempt_enable_notrace() at the end and this can call the same function again; exception_exit() is heavy and it is quite possible that need-resched is true again. 1. Change this code to dec preempt_count() and check need_resched() by hand. 2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid the enable/disable dance around __schedule(). But in this case we need to move into sched/core.c. 3. Cosmetic, but x86 forgets to declare this function. This doesn't really matter because it is only called by asm helpers, still it make sense to add the declaration into asm/preempt.h to match preempt_schedule(). Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Graf <agraf@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Christoph Lameter <cl@linux.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Chuck Ebbert <cebbert.lkml@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--arch/x86/include/asm/preempt.h1
-rw-r--r--kernel/context_tracking.c40
-rw-r--r--kernel/sched/core.c41
3 files changed, 42 insertions, 40 deletions
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 7024c12f7bfe..400873450e33 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -105,6 +105,7 @@ static __always_inline bool should_resched(void)
105# ifdef CONFIG_CONTEXT_TRACKING 105# ifdef CONFIG_CONTEXT_TRACKING
106 extern asmlinkage void ___preempt_schedule_context(void); 106 extern asmlinkage void ___preempt_schedule_context(void);
107# define __preempt_schedule_context() asm ("call ___preempt_schedule_context") 107# define __preempt_schedule_context() asm ("call ___preempt_schedule_context")
108 extern asmlinkage void preempt_schedule_context(void);
108# endif 109# endif
109#endif 110#endif
110 111
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 5664985c46a0..937ecdfdf258 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -107,46 +107,6 @@ void context_tracking_user_enter(void)
107} 107}
108NOKPROBE_SYMBOL(context_tracking_user_enter); 108NOKPROBE_SYMBOL(context_tracking_user_enter);
109 109
110#ifdef CONFIG_PREEMPT
111/**
112 * preempt_schedule_context - preempt_schedule called by tracing
113 *
114 * The tracing infrastructure uses preempt_enable_notrace to prevent
115 * recursion and tracing preempt enabling caused by the tracing
116 * infrastructure itself. But as tracing can happen in areas coming
117 * from userspace or just about to enter userspace, a preempt enable
118 * can occur before user_exit() is called. This will cause the scheduler
119 * to be called when the system is still in usermode.
120 *
121 * To prevent this, the preempt_enable_notrace will use this function
122 * instead of preempt_schedule() to exit user context if needed before
123 * calling the scheduler.
124 */
125asmlinkage __visible void __sched notrace preempt_schedule_context(void)
126{
127 enum ctx_state prev_ctx;
128
129 if (likely(!preemptible()))
130 return;
131
132 /*
133 * Need to disable preemption in case user_exit() is traced
134 * and the tracer calls preempt_enable_notrace() causing
135 * an infinite recursion.
136 */
137 preempt_disable_notrace();
138 prev_ctx = exception_enter();
139 preempt_enable_no_resched_notrace();
140
141 preempt_schedule();
142
143 preempt_disable_notrace();
144 exception_exit(prev_ctx);
145 preempt_enable_notrace();
146}
147EXPORT_SYMBOL_GPL(preempt_schedule_context);
148#endif /* CONFIG_PREEMPT */
149
150/** 110/**
151 * context_tracking_user_exit - Inform the context tracking that the CPU is 111 * context_tracking_user_exit - Inform the context tracking that the CPU is
152 * exiting userspace mode and entering the kernel. 112 * exiting userspace mode and entering the kernel.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index dde8adb7d0c0..240157c13ddc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2951,6 +2951,47 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
2951} 2951}
2952NOKPROBE_SYMBOL(preempt_schedule); 2952NOKPROBE_SYMBOL(preempt_schedule);
2953EXPORT_SYMBOL(preempt_schedule); 2953EXPORT_SYMBOL(preempt_schedule);
2954
2955#ifdef CONFIG_CONTEXT_TRACKING
2956/**
2957 * preempt_schedule_context - preempt_schedule called by tracing
2958 *
2959 * The tracing infrastructure uses preempt_enable_notrace to prevent
2960 * recursion and tracing preempt enabling caused by the tracing
2961 * infrastructure itself. But as tracing can happen in areas coming
2962 * from userspace or just about to enter userspace, a preempt enable
2963 * can occur before user_exit() is called. This will cause the scheduler
2964 * to be called when the system is still in usermode.
2965 *
2966 * To prevent this, the preempt_enable_notrace will use this function
2967 * instead of preempt_schedule() to exit user context if needed before
2968 * calling the scheduler.
2969 */
2970asmlinkage __visible void __sched notrace preempt_schedule_context(void)
2971{
2972 enum ctx_state prev_ctx;
2973
2974 if (likely(!preemptible()))
2975 return;
2976
2977 do {
2978 __preempt_count_add(PREEMPT_ACTIVE);
2979 /*
2980 * Needs preempt disabled in case user_exit() is traced
2981 * and the tracer calls preempt_enable_notrace() causing
2982 * an infinite recursion.
2983 */
2984 prev_ctx = exception_enter();
2985 __schedule();
2986 exception_exit(prev_ctx);
2987
2988 __preempt_count_sub(PREEMPT_ACTIVE);
2989 barrier();
2990 } while (need_resched());
2991}
2992EXPORT_SYMBOL_GPL(preempt_schedule_context);
2993#endif /* CONFIG_CONTEXT_TRACKING */
2994
2954#endif /* CONFIG_PREEMPT */ 2995#endif /* CONFIG_PREEMPT */
2955 2996
2956/* 2997/*