From: Paolo Bonzini <pbonzini@redhat.com>
To: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>,
qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org,
Christian Borntraeger <borntraeger@de.ibm.com>,
tu bo <tubo@linux.vnet.ibm.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
Date: Tue, 22 Mar 2016 13:11:05 +0100 [thread overview]
Message-ID: <56F13659.1020605@redhat.com> (raw)
In-Reply-To: <20160322125958.13afc4e7.cornelia.huck@de.ibm.com>
On 22/03/2016 12:59, Cornelia Huck wrote:
>> > They can be fixed with just an extra object_ref/object_unref.
>> >
>> > I didn't understand that Tu Bo also needed the BH fix, and with that
>> > information it makes sense. Passing the assign value ensures that
>> > ioeventfd remains always assigned. With the CPU threads out of the
>> > picture, the BH becomes enough to make everything thread-safe.
> Yes, this makes sense.
>
> Might we still have a hole somewhere in dataplane teardown? Probably
> not, from reading the code, even if it runs in cpu thread context.
The bug arises when the main thread sets started = true, a CPU thread
comes along while the ioeventfd is reset, and as soon as the BQL is
released by the main thread the CPU thread thinks it is a dataplane
thread. This does horrible things to non-reentrant code. For stop we
should be safe because the CPU thread is the one that sets started = false.
IOW, we should be safe as long as the ioeventfd is never unassigned
(your fix) _and_ we ensure serialization between threads that touch
dataplane_started (Fam's fix).
Paolo
next prev parent reply other threads:[~2016-03-22 12:11 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-16 10:10 [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop Fam Zheng
2016-03-16 10:10 ` [Qemu-devel] [PATCH 1/4] block: Use drained section in bdrv_set_aio_context Fam Zheng
2016-03-16 10:27 ` Paolo Bonzini
2016-03-16 10:51 ` Fam Zheng
2016-03-16 10:10 ` [Qemu-devel] [PATCH 2/4] block-backend: Introduce blk_drained_begin/end Fam Zheng
2016-03-16 10:10 ` [Qemu-devel] [PATCH 3/4] virtio-blk: Use blk_drained_begin/end around dataplane stop Fam Zheng
2016-03-16 10:10 ` [Qemu-devel] [PATCH 4/4] virtio-blk: Clean up start/stop with mutex and BH Fam Zheng
2016-03-17 15:00 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2016-03-17 15:07 ` Paolo Bonzini
2016-03-22 12:52 ` Fam Zheng
2016-03-22 18:05 ` Paolo Bonzini
2016-03-23 8:10 ` Cornelia Huck
2016-03-23 9:08 ` Paolo Bonzini
2016-03-23 9:12 ` Christian Borntraeger
2016-03-24 8:19 ` tu bo
2016-03-24 8:32 ` Cornelia Huck
2016-03-24 8:47 ` Cornelia Huck
2016-03-24 9:31 ` Cornelia Huck
2016-03-16 10:28 ` [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop Paolo Bonzini
2016-03-16 10:49 ` Christian Borntraeger
2016-03-16 11:09 ` Paolo Bonzini
2016-03-16 11:24 ` Christian Borntraeger
2016-03-16 12:55 ` Paolo Bonzini
2016-03-16 13:38 ` Christian Borntraeger
2016-03-16 13:45 ` Paolo Bonzini
2016-03-17 0:39 ` Fam Zheng
2016-03-17 11:03 ` tu bo
2016-03-21 10:57 ` Fam Zheng
2016-03-21 11:15 ` Cornelia Huck
2016-03-21 12:45 ` Fam Zheng
2016-03-21 13:02 ` Cornelia Huck
2016-03-21 23:45 ` Fam Zheng
2016-03-22 8:06 ` Cornelia Huck
2016-03-22 7:10 ` tu bo
2016-03-22 7:18 ` Fam Zheng
2016-03-22 9:07 ` Cornelia Huck
2016-03-22 9:46 ` Paolo Bonzini
2016-03-22 11:59 ` Cornelia Huck
2016-03-22 12:11 ` Paolo Bonzini [this message]
2016-03-22 12:54 ` Cornelia Huck
2016-03-17 12:22 ` tu bo
2016-03-17 12:39 ` Christian Borntraeger
2016-03-17 13:02 ` Cornelia Huck
2016-03-17 15:02 ` Paolo Bonzini
2016-03-17 15:07 ` Christian Borntraeger
2016-03-17 15:15 ` Christian Borntraeger
2016-03-17 15:16 ` Christian Borntraeger
2016-03-17 16:08 ` Christian Borntraeger
2016-03-18 15:03 ` Paolo Bonzini
2016-03-21 9:42 ` Fam Zheng
2016-03-21 11:10 ` Christian Borntraeger
2016-03-21 12:17 ` Cornelia Huck
2016-03-21 13:47 ` TU BO
2016-03-21 13:54 ` Paolo Bonzini
2016-03-21 14:19 ` Cornelia Huck
2016-03-22 0:31 ` Fam Zheng
2016-03-16 11:32 ` Cornelia Huck
2016-03-16 11:48 ` Paolo Bonzini
2016-03-16 11:56 ` Cornelia Huck
2016-03-16 11:59 ` Paolo Bonzini
2016-03-16 12:22 ` Cornelia Huck
2016-03-16 12:32 ` Paolo Bonzini
2016-03-16 12:42 ` Cornelia Huck
2016-03-16 12:49 ` Paolo Bonzini
2016-03-16 13:04 ` Cornelia Huck
2016-03-16 13:10 ` Paolo Bonzini
2016-03-16 13:14 ` Cornelia Huck
2016-03-16 13:15 ` Paolo Bonzini
2016-03-16 11:52 ` Cornelia Huck
2016-03-16 11:54 ` Paolo Bonzini
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