bpf: Provide recursion prevention helpers (c518cfa0) · Commits · 戴 / test

The places which need to prevent the execution of trace type BPF programs to prevent deadlocks on the hash bucket lock do this open coded. Provide two inline functions, bpf_disable/enable_instrumentation() to replace these open coded protection constructs. Use migrate_disable/enable() instead of preempt_disable/enable() right away so this works on RT enabled kernels. On a !RT kernel migrate_disable / enable() are mapped to preempt_disable/enable(). These helpers use this_cpu_inc/dec() instead of __this_cpu_inc/dec() on an RT enabled kernel because migrate disabled regions are preemptible and preemption might hit in the middle of a RMW operation which can lead to inconsistent state. Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200224145644.103910133@linutronix.de

include/linux/bpf.h

+30 −0

Original line number	Diff line number	Diff line
		@@ -961,6 +961,36 @@ _out: \
		#ifdef CONFIG_BPF_SYSCALL
		DECLARE_PER_CPU(int, bpf_prog_active);

		/*
		* Block execution of BPF programs attached to instrumentation (perf,
		* kprobes, tracepoints) to prevent deadlocks on map operations as any of
		* these events can happen inside a region which holds a map bucket lock
		* and can deadlock on it.
		*
		* Use the preemption safe inc/dec variants on RT because migrate disable
		* is preemptible on RT and preemption in the middle of the RMW operation
		* might lead to inconsistent state. Use the raw variants for non RT
		* kernels as migrate_disable() maps to preempt_disable() so the slightly
		* more expensive save operation can be avoided.
		*/
		static inline void bpf_disable_instrumentation(void)
		{
		migrate_disable();
		if (IS_ENABLED(CONFIG_PREEMPT_RT))
		this_cpu_inc(bpf_prog_active);
		else
		__this_cpu_inc(bpf_prog_active);
		}

		static inline void bpf_enable_instrumentation(void)
		{
		if (IS_ENABLED(CONFIG_PREEMPT_RT))
		this_cpu_dec(bpf_prog_active);
		else
		__this_cpu_dec(bpf_prog_active);
		migrate_enable();
		}

		extern const struct file_operations bpf_map_fops;
		extern const struct file_operations bpf_prog_fops;

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