From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: kwolf@redhat.com, famz@redhat.com, lersek@redhat.com,
qemu-devel@nongnu.org, rjones@redhat.com
Subject: Re: [Qemu-devel] [PATCH v2] AioContext: fix broken placement of event_notifier_test_and_clear
Date: Mon, 20 Jul 2015 21:50:01 +0200 [thread overview]
Message-ID: <55AD50E9.7060208@redhat.com> (raw)
In-Reply-To: <20150720163620.GN12675@stefanha-thinkpad.redhat.com>
On 20/07/2015 18:36, Stefan Hajnoczi wrote:
>> >
>> > i/o thread vcpu thread worker thread
>> > ---------------------------------------------------------------------
>> > lock_iothread
>> > notify_me = 1
>> > ...
>> > unlock_iothread
>> > lock_iothread
>> > notify_me = 3
>> > ppoll
>> > notify_me = 1
>> > bh->scheduled = 1
>> > event_notifier_set
>> > event_notifier_test_and_clear
>> > ppoll
>> > *** hang ***
> I don't understand this diagram. Why is event_notifier_test_and_clear()
> called by the vcpu thread? event_notifier_set() was called *after* vcpu
> thread's ppoll() returned so I wouldn't expect the vcpu thread to see
> the notify.
>
> Was there a previous notify pending?
Yes, for example a bottom half could have rescheduled itself.
Paolo
next prev parent reply other threads:[~2015-07-20 19:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-20 5:27 [Qemu-devel] [PATCH v2] AioContext: fix broken placement of event_notifier_test_and_clear Paolo Bonzini
2015-07-20 7:46 ` Fam Zheng
2015-07-20 10:06 ` Fam Zheng
2015-07-20 12:42 ` [Qemu-devel] R: " Paolo Bonzini
2015-07-21 1:19 ` [Qemu-devel] " Fam Zheng
2015-07-21 6:51 ` Paolo Bonzini
2015-07-20 16:36 ` Stefan Hajnoczi
2015-07-20 19:50 ` Paolo Bonzini [this message]
2015-07-21 11:04 ` Stefan Hajnoczi
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