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Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop

From: tu bo
Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
Date: Thu, 17 Mar 2016 19:03:10 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

On 03/17/2016 08:39 AM, Fam Zheng wrote:
On Wed, 03/16 14:45, Paolo Bonzini wrote:

On 16/03/2016 14:38, Christian Borntraeger wrote:
If you just remove the calls to virtio_queue_host_notifier_read, here
and in virtio_queue_aio_set_host_notifier_fd_handler, does it work
(keeping patches 2-4 in)?

With these changes and patch 2-4 it does no longer locks up.
I keep it running some hour to check if a crash happens.

Tu Bo, your setup is currently better suited for reproducing. Can you also 

Great, I'll prepare a patch to virtio then sketching the solution that
Conny agreed with.

While Fam and I agreed that patch 1 is not required, I'm not sure if the
mutex is necessary in the end.

If we can fix this from the virtio_queue_host_notifier_read side, the mutex/BH
are not necessary; but OTOH the mutex does catch such bugs, so maybe it's good
to have it. I'm not sure about the BH.

And on a hindsight I realize we don't want patches 2-3 too. Actually the
begin/end pair won't work as expected because of the blk_set_aio_context.

Let's hold on this series.

So if Tu Bo can check without the virtio_queue_host_notifier_read calls,
and both with/without Fam's patches, it would be great.

Tu Bo, only with/withoug patch 4, if you want to check. Sorry for the noise.

1. without the virtio_queue_host_notifier_read calls,  without patch 4

crash happens very often,

(gdb) bt
#0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
#1 0x000002aa165da37e in coroutine_trampoline (i0=<optimized out>, i1=1812051552) at util/coroutine-ucontext.c:79
#2  0x000003ff7dd5150a in __makecontext_ret () from /lib64/libc.so.6

2. without the virtio_queue_host_notifier_read calls, with patch 4

crash happens very often,

(gdb) bt
#0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
#1 0x000002aa39dda43e in coroutine_trampoline (i0=<optimized out>, i1=-1677715600) at util/coroutine-ucontext.c:79
#2  0x000003ffab6d150a in __makecontext_ret () from /lib64/libc.so.6


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