cleanup_workqueue_thread() in the CPU_DEAD and CPU_UP_CANCELLED path
will cause a deadlock if the worker thread is executing a work item
which is blocked on get_online_cpus(). This will lead to a irrecoverable
hang.
Solution is not to cleanup the worker thread. Instead let it remain
even after the cpu goes offline. Since no one can queue any work
on an offlined cpu, this thread will be forever sleeping, untill
someone onlines the cpu.
Signed-off-by: Gautham R Shenoy <[email protected]>
---
kernel/workqueue.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
Index: linux-2.6.23/kernel/workqueue.c
===================================================================
--- linux-2.6.23.orig/kernel/workqueue.c
+++ linux-2.6.23/kernel/workqueue.c
@@ -30,6 +30,7 @@
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
+#include <linux/cpumask.h>
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
@@ -679,6 +680,7 @@ init_cpu_workqueue(struct workqueue_stru
spin_lock_init(&cwq->lock);
INIT_LIST_HEAD(&cwq->worklist);
init_waitqueue_head(&cwq->more_work);
+ cwq->thread = NULL;
return cwq;
}
@@ -712,7 +714,7 @@ static void start_workqueue_thread(struc
if (p != NULL) {
if (cpu >= 0)
- kthread_bind(p, cpu);
+ set_cpus_allowed(p, cpumask_of_cpu(cpu));
wake_up_process(p);
}
}
@@ -848,6 +850,9 @@ static int __devinit workqueue_cpu_callb
switch (action) {
case CPU_UP_PREPARE:
+ if (likely(cwq->thread != NULL &&
+ !IS_ERR(cwq->thread)))
+ break;
if (!create_workqueue_thread(cwq, cpu))
break;
printk(KERN_ERR "workqueue [%s] for %i failed\n",
@@ -858,12 +863,6 @@ static int __devinit workqueue_cpu_callb
case CPU_ONLINE:
start_workqueue_thread(cwq, cpu);
break;
-
- case CPU_UP_CANCELED:
- start_workqueue_thread(cwq, -1);
- case CPU_DEAD:
- cleanup_workqueue_thread(cwq, cpu);
- break;
}
}
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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