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().

Oleg Nesterov committed 12 years ago

Commit 009f60e1 parent 64192653 files · +42 −40Browse files

Unified · Split

3 files

arch/x86/include/asm/preempt.h +1 −0
kernel/context_tracking.c +0 −40
kernel/sched/core.c +41 −0

arch/x86/include/asm/preempt.h+1−0

@@ -105,6 +105,7 @@ static __always_inline bool should_resched(void) · 104 unmodified lines
105	105	# ifdef CONFIG_CONTEXT_TRACKING
106	106	extern asmlinkage void ___preempt_schedule_context(void);
107	107	# define __preempt_schedule_context() asm ("call ___preempt_schedule_context")
	108	+ extern asmlinkage void preempt_schedule_context(void);
108	109	# endif
109	110	#endif
110	111

kernel/context_tracking.c+0−40

@@ -107,46 +107,6 @@ void context_tracking_user_enter(void) · 106 unmodified lines
107	107	}
108	108	NOKPROBE_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		− */
125		−asmlinkage __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		−}
147		−EXPORT_SYMBOL_GPL(preempt_schedule_context);
148		−#endif /* CONFIG_PREEMPT */
149		−
150	110	/**
151	111	* context_tracking_user_exit - Inform the context tracking that the CPU is
152	112	* exiting userspace mode and entering the kernel.

kernel/sched/core.c+41−0

@@ -2951,6 +2951,47 @@ asmlinkage __visible void __sched notrace preempt_schedule(void) · 2950 unmodified lines
2951	2951	}
2952	2952	NOKPROBE_SYMBOL(preempt_schedule);
2953	2953	EXPORT_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	+ */
	2970	+asmlinkage __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	+}
	2992	+EXPORT_SYMBOL_GPL(preempt_schedule_context);
	2993	+#endif /* CONFIG_CONTEXT_TRACKING */
	2994	+
2954	2995	#endif /* CONFIG_PREEMPT */
2955	2996
2956	2997	/*

sched: stop the unbound recursion in preempt_schedule_context()

Keyboard shortcuts

General

Issues and pull requests

Issues, pull requests and Inbox

Repository code