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Date: Tue, 16 Jul 2013 11:05:11 +0800
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130716030511.GF32278@stefanha-thinkpad.redhat.com>
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In-Reply-To: <1373917279-15360-1-git-send-email-borntraeger@de.ibm.com>
Subject: Re: [Qemu-devel] [PATCH 02/12] trace+libvirt: start trace
 processing thread in final child process
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To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: aliguori@us.ibm.com, =?iso-8859-1?Q?Llu=EDs?= <xscript@gmx.net>, Michael Mueller <mimu@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On Mon, Jul 15, 2013 at 09:41:19PM +0200, Christian Borntraeger wrote:
> When running with trace backend e.g. "simple" the writer thread needs to be
> implemented in the same process context as the trace points that will be
> processed. Under libvirtd control, qemu gets first started in daemonized
> mode to privide its capabilities. Creating the writer thread in the initial
> process context then leads to a dead lock because the thread gets termined
> together with the initial parent. (-daemonize) This results in
> stale qemu processes.
> Fix this by deferring trace initialization.

I don't think this works since trace events will fill up trace_buf[] and
eventually invoke flush_trace_file().

At that point we use trace_available_cond and trace_empty_cond, which
may be NULL in Glib <2.31.0.

Perhaps this can be made safe by checking trace_writeout_enabled.  It
will be false before the backend has been initialized.

Stefan