[Qemu-devel] [PATCH] tracing: start trace processing thread in final child process

[Qemu-devel] [PATCH] tracing: start trace processing thread in final child process

[Christian Borntraeger]

From: Michael Mueller <mimu@linux.vnet.ibm.com>

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)

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[minor whitespace fixes]
---
 vl.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/vl.c b/vl.c
index 4e709d5..93670c8 100644
--- a/vl.c
+++ b/vl.c
@@ -3863,8 +3863,10 @@ int main(int argc, char **argv, char **envp)
         qemu_set_log(mask);
     }
 
-    if (!trace_backend_init(trace_events, trace_file)) {
-        exit(1);
+    if (!is_daemonized()) {
+        if (!trace_backend_init(trace_events, trace_file)) {
+            exit(1);
+        }
     }
 
     /* If no data_dir is specified then try to find it relative to the
@@ -4358,6 +4360,12 @@ int main(int argc, char **argv, char **envp)
 
     os_setup_post();
 
+    if (is_daemonized()) {
+        if (!trace_backend_init(trace_events, trace_file)) {
+            exit(1);
+        }
+    }
+
     main_loop();
     bdrv_close_all();
     pause_all_vcpus();
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] tracing: start trace processing thread in final child process

[Stefan Hajnoczi]

On Mon, Sep 23, 2013 at 04:36:54PM +0200, Christian Borntraeger wrote:
> From: Michael Mueller <mimu@linux.vnet.ibm.com>
> 
> 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)
> 
> Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> [minor whitespace fixes]
> ---
>  vl.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

Thanks, applied to my tracing tree:
https://github.com/stefanha/qemu/commits/tracing

Stefan