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bpf/stackmap: Dont trylock mmap_sem with PREEMPT_RT and interrupts disabled
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
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@ -40,6 +40,9 @@ static void do_up_read(struct irq_work *entry)
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{
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struct stack_map_irq_work *work;
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if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
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return;
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work = container_of(entry, struct stack_map_irq_work, irq_work);
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up_read_non_owner(work->sem);
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work->sem = NULL;
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@ -288,10 +291,19 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
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struct stack_map_irq_work *work = NULL;
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if (irqs_disabled()) {
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work = this_cpu_ptr(&up_read_work);
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if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY)
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/* cannot queue more up_read, fallback */
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if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
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work = this_cpu_ptr(&up_read_work);
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if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY) {
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/* cannot queue more up_read, fallback */
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irq_work_busy = true;
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}
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} else {
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/*
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* PREEMPT_RT does not allow to trylock mmap sem in
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* interrupt disabled context. Force the fallback code.
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*/
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irq_work_busy = true;
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}
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}
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/*
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