[Xen-devel] Re: [PATCH] fix pgd_lock deadlock

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Tue, 15 Feb 2011, Andrea Arcangeli wrote:

> Hello,
> 
> Without this patch we can deadlock in the page_table_lock with NR_CPUS
> < 4 or THP on, with this patch we hopefully won't deadlock in the
> pgd_lock (if taken from irq). I can't see anything taking it from irq
> (maybe aio? to check I also tried the libaio testuite with no apparent
> VM_BUG_ON triggering), so unless somebody sees it, I think we should
> apply it. I've been running for a while with this patch applied
> without apparent problems. Other archs may follow suit if it's proven
> that there's nothing taking the pgd_lock from irq.
> 
> ===
> Subject: fix pgd_lock deadlock
> 
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> 
> It's forbidden to take the page_table_lock with the irq disabled or if there's
> contention the IPIs (for tlb flushes) sent with the page_table_lock held will
> never run leading to a deadlock.

I really read this thing 5 times and still cannot make any sense of it.

You talk about page_table_lock and then fiddle with pgd_lock.

-ENOSENSE

        tglx

 

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