Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] target/ppc: Fix system lockups caused by interrupt_request state corruption

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Dec 04, 2017 at 12:00:40PM +1100, David Gibson wrote:
> On Fri, Dec 01, 2017 at 03:49:07PM +0000, Richard Purdie wrote:
> > Occasionally in Linux guests on x86_64 we're seeing logs like:
> > 
> > ppc_set_irq: 0x55b4e0d562f0 n_IRQ 8 level 1 => pending 00000100req 00000004
> > 
> > when they should read:
> > 
> > ppc_set_irq: 0x55b4e0d562f0 n_IRQ 8 level 1 => pending 00000100req 00000002
> > 
> > The "00000004" is CPU_INTERRUPT_EXITTB yet the code calls
> > cpu_interrupt(cs, CPU_INTERRUPT_HARD) ("00000002") in this function
> > just before the log message. Something is causing the HARD bit setting
> > to get lost.
> > 
> > The knock on effect of losing that bit is the decrementer timer interrupts
> > don't get delivered which causes the guest to sit idle in its idle handler
> > and 'hang'.
> > 
> > The issue occurs due to races from code which sets CPU_INTERRUPT_EXITTB.
> > 
> > Rather than poking directly into cs->interrupt_request, that code needs to:
> > 
> > a) hold BQL
> > b) use the cpu_interrupt() helper
> > 
> > This patch fixes the call sites to do this, fixing the hang.
> > 
> > Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> 
> I strongly suspect there's a better way to do this long term - a lot
> of that old ppc TCG code is really crufty.  But as best I can tell,
> this is certainly a fix over what we had.  So, applied to
> ppc-for-2.11.

I take that back.  Running make check with this patch results in:

  GTESTER check-qtest-ppc64
**
ERROR:/home/dwg/src/qemu/cpus.c:1582:qemu_mutex_lock_iothread: assertion failed: (!qemu_mutex_iothread_locked())
Broken pipe
qemu-system-ppc64: RP: Received invalid message 0x0000 length 0x0000
GTester: last random seed: R02S895b0f4813776bf68c147bf987e73f7b
make: *** [/home/dwg/src/qemu/tests/Makefile.include:852: check-qtest-ppc64] Error 1

So, I've reverted it.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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