From 25b9c7f9756ce3a16a95f5f15fd0969ce5bbaf4f Mon Sep 17 00:00:00 2001
From: Ben Gamari <ben@smart-cactus.org>
Date: Tue, 1 Oct 2019 22:23:03 +0000
Subject: [PATCH] rts: Pause timer while changing capability count
This avoids #17289.
---
rts/Schedule.c | 8 ++++++++
rts/Timer.c | 24 +++++++++++++-----------
2 files changed, 21 insertions(+), 11 deletions(-)
diff --git a/rts/Schedule.c b/rts/Schedule.c
index f97777927a5f..061de639b28f 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -2229,6 +2229,12 @@ setNumCapabilities (uint32_t new_n_capabilities USED_IF_THREADS)
cap = rts_lock();
task = cap->running_task;
+
+ // N.B. We must stop the interval timer while we are changing the
+ // capabilities array lest handle_tick may try to context switch
+ // an old capability. See #17289.
+ stopTimer();
+
stopAllCapabilities(&cap, task);
if (new_n_capabilities < enabled_capabilities)
@@ -2311,6 +2317,8 @@ setNumCapabilities (uint32_t new_n_capabilities USED_IF_THREADS)
// Notify IO manager that the number of capabilities has changed.
rts_evalIO(&cap, ioManagerCapabilitiesChanged_closure, NULL);
+ startTimer();
+
rts_unlock(cap);
#endif // THREADED_RTS
diff --git a/rts/Timer.c b/rts/Timer.c
index b21bddbcfa37..c44390574278 100644
--- a/rts/Timer.c
+++ b/rts/Timer.c
@@ -25,6 +25,15 @@
#include "Capability.h"
#include "RtsSignals.h"
+// This global counter is used to allow multiple threads to stop the
+// timer temporarily with a stopTimer()/startTimer() pair. If
+// timer_enabled == 0 timer is enabled
+// timer_disabled == N, N > 0 timer is disabled by N threads
+// When timer_enabled makes a transition to 0, we enable the timer,
+// and when it makes a transition to non-0 we disable it.
+
+static StgWord timer_disabled;
+
/* ticks left before next pre-emptive context switch */
static int ticks_to_ctxt_switch = 0;
@@ -45,7 +54,9 @@ void
handle_tick(int unused STG_UNUSED)
{
handleProfTick();
- if (RtsFlags.ConcFlags.ctxtSwitchTicks > 0) {
+ if (RtsFlags.ConcFlags.ctxtSwitchTicks > 0
+ && RELAXED_LOAD(&timer_disabled) == 0)
+ {
ticks_to_ctxt_switch--;
if (ticks_to_ctxt_switch <= 0) {
ticks_to_ctxt_switch = RtsFlags.ConcFlags.ctxtSwitchTicks;
@@ -101,15 +112,6 @@ handle_tick(int unused STG_UNUSED)
}
}
-// This global counter is used to allow multiple threads to stop the
-// timer temporarily with a stopTimer()/startTimer() pair. If
-// timer_enabled == 0 timer is enabled
-// timer_disabled == N, N > 0 timer is disabled by N threads
-// When timer_enabled makes a transition to 0, we enable the timer,
-// and when it makes a transition to non-0 we disable it.
-
-static StgWord timer_disabled;
-
void
initTimer(void)
{
@@ -117,7 +119,7 @@ initTimer(void)
if (RtsFlags.MiscFlags.tickInterval != 0) {
initTicker(RtsFlags.MiscFlags.tickInterval, handle_tick);
}
- timer_disabled = 1;
+ RELAXED_STORE(&timer_disabled, 1);
}
void
--
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