>From 40f5100cb73aad8f90ba2c926dd08c4e15789de0 Mon Sep 17 00:00:00 2001
From: Nikhil Mahale <[email protected]>
Date: Tue, 11 Nov 2014 17:44:28 +0530
Subject: [PATCH] os: Fix timer race conditions
Fixing following kind of race-conditions -
WaitForSomething()
|
----> // timers -> timer-1 -> timer-2 -> null
while (timers && (int) (timers->expires - now) <= 0)
// prototype - DoTimer(OsTimerPtr timer, CARD32 now, OsTimerPtr *prev)
DoTimer(timers, now, &timers)
|
|
----> OsBlockSignals(); .... OS Signal comes just before blocking it,
.... timer-1 handler gets called.
// timer-1 gets served and scheduled again;
// timers -> timer-2 -> timer-1 -> null
....
*prev = timer->next;
timer->next = NULL; // timers -> null
// timers list gets corrupted here and timer-2 gets removed from list.
https://bugs.freedesktop.org/show_bug.cgi?id=86288
Signed-off-by: Nikhil Mahale <[email protected]>
---
os/WaitFor.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)
diff --git a/os/WaitFor.c b/os/WaitFor.c
index 39fedd9..6e54222 100644
--- a/os/WaitFor.c
+++ b/os/WaitFor.c
@@ -123,7 +123,7 @@ struct _OsTimerRec {
static void DoTimer(OsTimerPtr timer, CARD32 now, OsTimerPtr *prev);
static void CheckAllTimers(void);
-static OsTimerPtr timers = NULL;
+static volatile OsTimerPtr timers = NULL;
/*****************
* WaitForSomething:
@@ -263,11 +263,14 @@ WaitForSomething(int *pClientsReady)
if ((int) (timers->expires - now) <= 0)
expired = 1;
- while (timers && (int) (timers->expires - now) <= 0)
- DoTimer(timers, now, &timers);
+ if (expired) {
+ OsBlockSignals();
+ while (timers && (int) (timers->expires - now) <= 0)
+ DoTimer(timers, now, &timers);
+ OsReleaseSignals();
- if (expired)
return 0;
+ }
}
}
else {
@@ -281,11 +284,14 @@ WaitForSomething(int *pClientsReady)
if ((int) (timers->expires - now) <= 0)
expired = 1;
- while (timers && (int) (timers->expires - now) <= 0)
- DoTimer(timers, now, &timers);
+ if (expired) {
+ OsBlockSignals();
+ while (timers && (int) (timers->expires - now) <= 0)
+ DoTimer(timers, now, &timers);
+ OsReleaseSignals();
- if (expired)
return 0;
+ }
}
}
if (someReady)
@@ -408,10 +414,11 @@ DoTimer(OsTimerPtr timer, CARD32 now, OsTimerPtr *prev)
OsBlockSignals();
*prev = timer->next;
timer->next = NULL;
+ OsReleaseSignals();
+
newTime = (*timer->callback) (timer, now, timer->arg);
if (newTime)
TimerSet(timer, 0, newTime, timer->callback, timer->arg);
- OsReleaseSignals();
}
OsTimerPtr
@@ -515,8 +522,12 @@ TimerCheck(void)
{
CARD32 now = GetTimeInMillis();
- while (timers && (int) (timers->expires - now) <= 0)
- DoTimer(timers, now, &timers);
+ if (timers && (int) (timers->expires - now) <= 0) {
+ OsBlockSignals();
+ while (timers && (int) (timers->expires - now) <= 0)
+ DoTimer(timers, now, &timers);
+ OsReleaseSignals();
+ }
}
void
--
1.8.1.5
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