Subject: + cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5.patch added to -mm tree
To: srivatsa.bhat@xxxxxxxxxxxxxxxxxx,bp@xxxxxxx,ego@xxxxxxxxxxxxxxxxxx,fweisbec@xxxxxxxxx,hch@xxxxxxxxxxxxx,mgalbraith@xxxxxxx,mgorman@xxxxxxx,mingo@xxxxxxxxxx,oleg@xxxxxxxxxx,paulmck@xxxxxxxxxxxxxxxxxx,peterz@xxxxxxxxxxxxx,riel@xxxxxxxxxx,rjw@xxxxxxxxxxxxx,rostedt@xxxxxxxxxxx,rusty@xxxxxxxxxxxxxxx,tglx@xxxxxxxxxxxxx,tj@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Thu, 15 May 2014 14:59:37 -0700
The patch titled
Subject: cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5
has been added to the -mm tree. Its filename is
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5.patch
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------------------------------------------------------
From: "Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Subject: cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mike Galbraith <mgalbraith@xxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/stop_machine.c | 38 ++++++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 14 deletions(-)
diff -puN kernel/stop_machine.c~cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5 kernel/stop_machine.c
--- a/kernel/stop_machine.c~cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5
+++ a/kernel/stop_machine.c
@@ -193,27 +193,37 @@ static int multi_cpu_stop(void *data)
cpu_relax();
/*
- * In the case of CPU offline, we don't want the other CPUs to
- * send IPIs to the active_cpu (the one going offline) after it
- * has disabled interrupts in the _DISABLE_IRQ state (because,
- * then it will notice the IPIs only after it goes offline). So
- * we split this state into _INACTIVE and _ACTIVE, and thereby
- * ensure that the active_cpu disables interrupts only after
- * the other CPUs do the same thing.
+ * We use 2 separate stages to disable interrupts, namely
+ * _INACTIVE and _ACTIVE, to ensure that the inactive CPUs
+ * disable their interrupts first, followed by the active CPUs.
+ *
+ * This is done to avoid a race in the CPU offline path, which
+ * can lead to receiving IPIs on the outgoing CPU *after* it
+ * has gone offline.
+ *
+ * During CPU offline, we don't want the other CPUs to send
+ * IPIs to the active_cpu (the outgoing CPU) *after* it has
+ * disabled interrupts (because, then it will notice the IPIs
+ * only after it has gone offline). We can prevent this by
+ * making the other CPUs disable their interrupts first - that
+ * way, they will run the stop-machine code with interrupts
+ * disabled, and hence won't send IPIs after that point.
*/
if (msdata->state != curstate) {
curstate = msdata->state;
switch (curstate) {
case MULTI_STOP_DISABLE_IRQ_INACTIVE:
- if (is_active)
- break;
-
- /* Else, fall-through */
-
+ if (!is_active) {
+ local_irq_disable();
+ hard_irq_disable();
+ }
+ break;
case MULTI_STOP_DISABLE_IRQ_ACTIVE:
- local_irq_disable();
- hard_irq_disable();
+ if (is_active) {
+ local_irq_disable();
+ hard_irq_disable();
+ }
break;
case MULTI_STOP_RUN:
if (is_active)
_
Patches currently in -mm which might be from srivatsa.bhat@xxxxxxxxxxxxxxxxxx are
smp-print-more-useful-debug-info-upon-receiving-ipi-on-an-offline-cpu.patch
smp-print-more-useful-debug-info-upon-receiving-ipi-on-an-offline-cpu-fix.patch
smp-print-more-useful-debug-info-upon-receiving-ipi-on-an-offline-cpu-v5.patch
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu.patch
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v3.patch
cpu-hotplug-stop-machine-plug-race-window-that-leads-to-ipi-to-offline-cpu-v5.patch
cpu-hotplug-smp-flush-any-pending-ipi-callbacks-before-cpu-offline.patch
linux-next.patch
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