linux-kernel - Re: [PATCH v5 1/4] kvm: Extend irqfd to support level interrupts

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Message-ID: <20120718213043.GB11738@redhat.com>
Date:	Thu, 19 Jul 2012 00:30:43 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, avi@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	jan.kiszka@...mens.com
Subject: Re: [PATCH v5 1/4] kvm: Extend irqfd to support level interrupts

On Wed, Jul 18, 2012 at 06:23:34PM -0300, Marcelo Tosatti wrote:
> On Wed, Jul 18, 2012 at 02:28:34PM -0600, Alex Williamson wrote:
> > > turn on lockdep to remember why I couldn't sleep there.
> > 
> > switching to a mutex results in:
> > 
> > BUG: sleeping function called from invalid context at kernel/mutex.c:269
> > in_atomic(): 1, irqs_disabled(): 0, pid: 30025, name: qemu-system-x86
> > INFO: lockdep is turned off.
> > Pid: 30025, comm: qemu-system-x86 Not tainted 3.5.0-rc4+ #109
> > Call Trace:
> >  [<ffffffff81088425>] __might_sleep+0xf5/0x130
> >  [<ffffffff81564c6f>] mutex_lock_nested+0x2f/0x60
> >  [<ffffffffa07db7d5>] eoifd_event+0x25/0x70 [kvm]
> >  [<ffffffffa07daea4>] kvm_notify_acked_irq+0xa4/0x140 [kvm]
> >  [<ffffffffa07dae2a>] ? kvm_notify_acked_irq+0x2a/0x140 [kvm]
> >  [<ffffffffa07d9bb4>] kvm_ioapic_update_eoi+0x84/0xf0 [kvm]
> >  [<ffffffffa0806c43>] apic_set_eoi+0x123/0x130 [kvm]
> >  [<ffffffffa0806fd8>] apic_reg_write+0x388/0x670 [kvm]
> >  [<ffffffffa07eb03c>] ? vcpu_enter_guest+0x32c/0x740 [kvm]
> >  [<ffffffffa0807481>] kvm_lapic_set_eoi+0x21/0x30 [kvm]
> >  [<ffffffffa04ba3f9>] handle_apic_access+0x69/0x80 [kvm_intel]
> >  [<ffffffffa04ba02a>] vmx_handle_exit+0xaa/0x260 [kvm_intel]
> 
> Its RCU from ack notifiers, OK. 

I'm testing a patch that moves all bitmap handling to under
pic/ioapic lock. After this we can teach kvm_set_irq to report
when a bit that is cleared/set is already clear/set, without
races.

And then no tracking will be necessary in irqfd - we can just
call kvm_set_irq(..., 0) and look at the return status.

-- 
MST
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