bpf/stackmap: Dont trylock mmap_sem with PREEMPT_RT and interrupts disabled (099bfaa7) · Commits · 戴 / test

In a RT kernel down_read_trylock() cannot be used from NMI context and up_read_non_owner() is another problematic issue. So in such a configuration, simply elide the annotated stackmap and just report the raw IPs. In the longer term, it might be possible to provide a atomic friendly versions of the page cache traversal which will at least provide the info if the pages are resident and don't need to be paged in. [ tglx: Use IS_ENABLED() to avoid the #ifdeffery, fixup the irq work callback and add a comment ] Signed-off-by:

David S. Miller <davem@davemloft.net> Signed-off-by:

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

Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200224145644.708960317@linutronix.de

kernel/bpf/stackmap.c

+15 −3

Original line number	Diff line number	Diff line
		@@ -40,6 +40,9 @@ static void do_up_read(struct irq_work *entry)
		{
		struct stack_map_irq_work *work;

		if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
		return;

		work = container_of(entry, struct stack_map_irq_work, irq_work);
		up_read_non_owner(work->sem);
		work->sem = NULL;
		@@ -288,11 +291,20 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
		struct stack_map_irq_work *work = NULL;

		if (irqs_disabled()) {
		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
		work = this_cpu_ptr(&up_read_work);
		if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY)
		if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY) {
		/* cannot queue more up_read, fallback */
		irq_work_busy = true;
		}
		} else {
		/*
		* PREEMPT_RT does not allow to trylock mmap sem in
		* interrupt disabled context. Force the fallback code.
		*/
		irq_work_busy = true;
		}
		}

		/*
		* We cannot do up_read() when the irq is disabled, because of

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