[Xen-devel] [PATCH][QEMU] Make active-timers thread-safe

[Ben Guthro <bguthro@xxxxxxxxxxxxxxx>]

Protect active_timers[] lists with mutexes so timers can be safely used from 
different threads.

Signed-off-by: Ben Guthro <bguthro@xxxxxxxxxxxxxx>
Signed-off-by: Gary Grebus <ggrebus@xxxxxxxxxxxxxxx>

diff -r 475eda44cd99 tools/ioemu/vl.c
--- a/tools/ioemu/vl.c  Mon Aug 27 14:14:56 2007 -0400
+++ b/tools/ioemu/vl.c  Mon Aug 27 14:14:56 2007 -0400
@@ -759,6 +759,7 @@ QEMUClock *vm_clock;
 QEMUClock *vm_clock;
 
 static QEMUTimer *active_timers[2];
+static pthread_mutex_t active_timers_lock[2];
 #ifdef _WIN32
 static MMRESULT timerID;
 static HANDLE host_alarm = NULL;
@@ -795,7 +796,7 @@ void qemu_free_timer(QEMUTimer *ts)
 }
 
 /* stop a timer, but do not dealloc it */
-void qemu_del_timer(QEMUTimer *ts)
+static void qemu_del_timer_nolock(QEMUTimer *ts)
 {
     QEMUTimer **pt, *t;
 
@@ -808,10 +809,18 @@ void qemu_del_timer(QEMUTimer *ts)
             break;
         if (t == ts) {
             *pt = t->next;
+           t->next = NULL;
             break;
         }
         pt = &t->next;
     }
+}
+
+void qemu_del_timer(QEMUTimer *ts)
+{
+    pthread_mutex_lock(&active_timers_lock[ts->clock->type]);
+    qemu_del_timer_nolock(ts);
+    pthread_mutex_unlock(&active_timers_lock[ts->clock->type]);
 }
 
 void qemu_advance_timer(QEMUTimer *ts, int64_t expire_time)
@@ -826,11 +835,13 @@ void qemu_mod_timer(QEMUTimer *ts, int64
 {
     QEMUTimer **pt, *t;
 
-    qemu_del_timer(ts);
-
-    /* add the timer in the sorted list */
     /* NOTE: this code must be signal safe because
        qemu_timer_expired() can be called from a signal. */
+    pthread_mutex_lock(&active_timers_lock[ts->clock->type]);
+
+    qemu_del_timer_nolock(ts);
+
+    /* add the timer in the sorted list */
     pt = &active_timers[ts->clock->type];
     for(;;) {
         t = *pt;
@@ -843,16 +854,20 @@ void qemu_mod_timer(QEMUTimer *ts, int64
     ts->expire_time = expire_time;
     ts->next = *pt;
     *pt = ts;
+    pthread_mutex_unlock(&active_timers_lock[ts->clock->type]);
 }
 
 int qemu_timer_pending(QEMUTimer *ts)
 {
     QEMUTimer *t;
+    pthread_mutex_lock(&active_timers_lock[ts->clock->type]);
     for(t = active_timers[ts->clock->type]; t != NULL; t = t->next) {
         if (t == ts)
-            return 1;
-    }
-    return 0;
+            break;
+    }
+    pthread_mutex_unlock(&active_timers_lock[ts->clock->type]);
+    return !!t;
+
 }
 
 static inline int qemu_timer_expired(QEMUTimer *timer_head, int64_t 
current_time)
@@ -865,7 +880,12 @@ static void qemu_run_timers(QEMUTimer **
 static void qemu_run_timers(QEMUTimer **ptimer_head, int64_t current_time)
 {
     QEMUTimer *ts;
+    int clock_type;
     
+    if (*ptimer_head == NULL)
+       return;
+    clock_type = (*ptimer_head)->clock->type;
+    pthread_mutex_lock(&active_timers_lock[clock_type]);
     for(;;) {
         ts = *ptimer_head;
         if (!ts || ts->expire_time > current_time)
@@ -875,8 +895,11 @@ static void qemu_run_timers(QEMUTimer **
         ts->next = NULL;
         
         /* run the callback (the timer list can be modified) */
+       pthread_mutex_unlock(&active_timers_lock[clock_type]);
         ts->cb(ts->opaque);
-    }
+       pthread_mutex_lock(&active_timers_lock[clock_type]);
+    }
+    pthread_mutex_unlock(&active_timers_lock[clock_type]);
 }
 
 int64_t qemu_get_clock(QEMUClock *clock)

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