[Qemu-devel] [PATCH v7 12/23] monitor: let suspend_cnt be thread safe

2018-01-23 Thread Peter Xu 
Monitor code now can be run in more than one thread.  Let it be thread
safe when accessing suspend_cnt counter.

Reviewed-by: Eric Blake 
Signed-off-by: Peter Xu 
---
 monitor.c | 15 ---
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/monitor.c b/monitor.c
index 92114aaa80..60bcf67b3a 100644
--- a/monitor.c
+++ b/monitor.c
@@ -190,7 +190,7 @@ struct Monitor {
 CharBackend chr;
 int reset_seen;
 int flags;
-int suspend_cnt;
+int suspend_cnt;/* Needs to be accessed atomically */
 bool skip_flush;
 bool use_io_thr;
 
@@ -3864,7 +3864,7 @@ static int monitor_can_read(void *opaque)
 {
 Monitor *mon = opaque;
 
-return (mon->suspend_cnt == 0) ? 1 : 0;
+return !atomic_mb_read(&mon->suspend_cnt);
 }
 
 /*
@@ -3996,7 +3996,7 @@ int monitor_suspend(Monitor *mon)
 {
 if (!mon->rs)
 return -ENOTTY;
-mon->suspend_cnt++;
+atomic_inc(&mon->suspend_cnt);
 return 0;
 }
 
@@ -4004,8 +4004,9 @@ void monitor_resume(Monitor *mon)
 {
 if (!mon->rs)
 return;
-if (--mon->suspend_cnt == 0)
+if (atomic_dec_fetch(&mon->suspend_cnt) == 0) {
 readline_show_prompt(mon->rs);
+}
 }
 
 static QObject *get_qmp_greeting(Monitor *mon)
@@ -4070,19 +4071,19 @@ static void monitor_event(void *opaque, int event)
 monitor_resume(mon);
 monitor_flush(mon);
 } else {
-mon->suspend_cnt = 0;
+atomic_mb_set(&mon->suspend_cnt, 0);
 }
 break;
 
 case CHR_EVENT_MUX_OUT:
 if (mon->reset_seen) {
-if (mon->suspend_cnt == 0) {
+if (atomic_mb_read(&mon->suspend_cnt) == 0) {
 monitor_printf(mon, "\n");
 }
 monitor_flush(mon);
 monitor_suspend(mon);
 } else {
-mon->suspend_cnt++;
+atomic_inc(&mon->suspend_cnt);
 }
 qemu_mutex_lock(&mon->out_lock);
 mon->mux_out = 1;
-- 
2.14.3

Re: [Qemu-devel] [PATCH v7 12/23] monitor: let suspend_cnt be thread safe

2018-02-21 Thread Stefan Hajnoczi 
On Wed, Jan 24, 2018 at 01:39:46PM +0800, Peter Xu wrote:
> @@ -3996,7 +3996,7 @@ int monitor_suspend(Monitor *mon)
>  {
>  if (!mon->rs)
>  return -ENOTTY;

Does this mean that QMP monitors like -qmp unix:/tmp/foo,server,nowait
will not use suspend_cnt?

I thought the point was to use suspend_cnt for QMP monitors too.


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Re: [Qemu-devel] [PATCH v7 12/23] monitor: let suspend_cnt be thread safe

2018-02-21 Thread Stefan Hajnoczi 
On Wed, Jan 24, 2018 at 01:39:46PM +0800, Peter Xu wrote:
> Monitor code now can be run in more than one thread.  Let it be thread
> safe when accessing suspend_cnt counter.
> 
> Reviewed-by: Eric Blake 
> Signed-off-by: Peter Xu 
> ---
>  monitor.c | 15 ---
>  1 file changed, 8 insertions(+), 7 deletions(-)

Reviewed-by: Stefan Hajnoczi 


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Re: [Qemu-devel] [PATCH v7 12/23] monitor: let suspend_cnt be thread safe

2018-02-21 Thread Stefan Hajnoczi 
Nevermind, I see the next patch adds QMP support.

Stefan


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