[Xen-devel] [Question] Is it safe to call "xmalloc()" with irq disabled?

[Haitao Shan <maillists.shan@xxxxxxxxx>]

Hi, Keir,

In recent effort on debugging cpu offline/online, I met Xen panic some times.

The reason of the panic is caused by following code path:

xmalloc ---> alloc_heap_pages ---> flush_area_mask { ASSERT(local_irq_enabled)........}

This bring me the question: is it safe to call xmalloc with local irq disabled? As you can see, not all alloc_heap_pages will result in TLB flushing. But once it calls, the assertion will fail.

In my case, the xmalloc is called with starting secondary processors. Some initialization code run with local irq enabled, for example, the MCA initialization. Normally this piece of code runs when all heap pages do not have a former owner (no domain is initialized at booting time, I guess), so calling xmalloc won't be a problem. But later when this same piece of code runs as a result of cpu online operation, it has possibility to trigger the assertion failure.

What's you view on this, Keir? Is it the design that xmalloc must be called with local irq enabled? I have done a hack to remove the assertion. Every things work just fine to me. But maybe I just happened not to run into any problem with the hack.

Shan Haitao

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