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Re: [Qemu-block] [PATCH] throttle-groups: fix hang when group member lea

From: Alberto Garcia
Subject: Re: [Qemu-block] [PATCH] throttle-groups: fix hang when group member leaves
Date: Wed, 01 Aug 2018 16:45:36 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Tue 31 Jul 2018 06:47:53 PM CEST, Alberto Garcia wrote:
> On Wed 04 Jul 2018 04:54:10 PM CEST, Stefan Hajnoczi wrote:
>> Throttle groups consist of members sharing one throttling state
>> (including bps/iops limits).  Round-robin scheduling is used to ensure
>> fairness.  If a group member already has a timer pending then other
>> groups members do not schedule their own timers.  The next group
>> member will have its turn when the existing timer expires.
>> A hang may occur when a group member leaves while it had a timer
>> scheduled.
> Ok, I can reproduce this if I run fio with iodepth=1.

I managed to write a test case for this, but unfortunately it seems that
this patch is not enough and it's still possible to hang QEMU 3.0.0-rc2.

I expect to have a fix for tomorrow.


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