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SubjectRe: [BUG][2.5.66bk9+] - tty hangings - patches, dmesg & sysctl+T info
"Shawn Starr" <spstarr@sh0n.net> wrote:
>
> login D C7250C94 4191040372 115 1 116 113 (L-TLB)
> Call Trace:
> [<c01394a5>] flush_workqueue+0x305/0x450
> [<c011de30>] default_wake_function+0x0/0x20
> [<c011de30>] default_wake_function+0x0/0x20
> [<c0257a44>] release_dev+0x6a4/0x860
> [<c010cd75>] do_IRQ+0x235/0x370
> [<c0258204>] tty_release+0x94/0x1b0
> [<c016dd7c>] __fput+0xac/0x100
> [<c0258170>] tty_release+0x0/0x1b0
> [<c016ddcb>] __fput+0xfb/0x100

Well it does look like you've hit the flush_workqueue livelock.

Can you run with this (rather hastily tested) patch?


kernel/workqueue.c | 80 ++++++++++++++++++++++++++---------------------------
1 files changed, 40 insertions(+), 40 deletions(-)
diff -puN kernel/workqueue.c~flush_workqueue-hang-fix kernel/workqueue.c
--- 25/kernel/workqueue.c~flush_workqueue-hang-fix 2003-04-08 20:23:22.000000000 -0700
+++ 25-akpm/kernel/workqueue.c 2003-04-08 21:02:10.000000000 -0700
@@ -27,13 +27,20 @@
#include <linux/slab.h>

/*
- * The per-CPU workqueue:
+ * The per-CPU workqueue.
+ *
+ * The sequnece counters are for flush_scheduled_work(). It wants to wait
+ * until until all currently-scheduled works are completed, but it doesn't
+ * want to be livelocked by new, incoming ones. So it waits until
+ * remove_sequence is >= the initial insert_sequence
*/
struct cpu_workqueue_struct {

spinlock_t lock;

- atomic_t nr_queued;
+ long remove_sequence; /* Least-recently added (next to run) */
+ long insert_sequence; /* Next to add */
+
struct list_head worklist;
wait_queue_head_t more_work;
wait_queue_head_t work_done;
@@ -71,10 +78,9 @@ int queue_work(struct workqueue_struct *

spin_lock_irqsave(&cwq->lock, flags);
list_add_tail(&work->entry, &cwq->worklist);
- atomic_inc(&cwq->nr_queued);
- spin_unlock_irqrestore(&cwq->lock, flags);
-
+ cwq->insert_sequence++;
wake_up(&cwq->more_work);
+ spin_unlock_irqrestore(&cwq->lock, flags);
ret = 1;
}
put_cpu();
@@ -93,11 +99,13 @@ static void delayed_work_timer_fn(unsign
*/
spin_lock_irqsave(&cwq->lock, flags);
list_add_tail(&work->entry, &cwq->worklist);
+ cwq->insert_sequence++;
wake_up(&cwq->more_work);
spin_unlock_irqrestore(&cwq->lock, flags);
}

-int queue_delayed_work(struct workqueue_struct *wq, struct work_struct *work, unsigned long delay)
+int queue_delayed_work(struct workqueue_struct *wq,
+ struct work_struct *work, unsigned long delay)
{
int ret = 0, cpu = get_cpu();
struct timer_list *timer = &work->timer;
@@ -107,18 +115,11 @@ int queue_delayed_work(struct workqueue_
BUG_ON(timer_pending(timer));
BUG_ON(!list_empty(&work->entry));

- /*
- * Increase nr_queued so that the flush function
- * knows that there's something pending.
- */
- atomic_inc(&cwq->nr_queued);
work->wq_data = cwq;
-
timer->expires = jiffies + delay;
timer->data = (unsigned long)work;
timer->function = delayed_work_timer_fn;
add_timer(timer);
-
ret = 1;
}
put_cpu();
@@ -135,7 +136,8 @@ static inline void run_workqueue(struct
*/
spin_lock_irqsave(&cwq->lock, flags);
while (!list_empty(&cwq->worklist)) {
- struct work_struct *work = list_entry(cwq->worklist.next, struct work_struct, entry);
+ struct work_struct *work = list_entry(cwq->worklist.next,
+ struct work_struct, entry);
void (*f) (void *) = work->func;
void *data = work->data;

@@ -146,14 +148,9 @@ static inline void run_workqueue(struct
clear_bit(0, &work->pending);
f(data);

- /*
- * We only wake up 'work done' waiters (flush) when
- * the last function has been fully processed.
- */
- if (atomic_dec_and_test(&cwq->nr_queued))
- wake_up(&cwq->work_done);
-
spin_lock_irqsave(&cwq->lock, flags);
+ cwq->remove_sequence++;
+ wake_up(&cwq->work_done);
}
spin_unlock_irqrestore(&cwq->lock, flags);
}
@@ -223,8 +220,13 @@ static int worker_thread(void *__startup
* Forces execution of the workqueue and blocks until its completion.
* This is typically used in driver shutdown handlers.
*
- * NOTE: if work is being added to the queue constantly by some other
- * context then this function might block indefinitely.
+ * This function will sample each workqueue's current insert_sequence number and
+ * will sleep until the head sequence is greater than or equal to that. This
+ * means that we sleep until all works which were queued on entry have been
+ * handled, but we are not livelocked by new incoming ones.
+ *
+ * This function used to run the workqueues itself. Now we just wait for the
+ * helper threads to do it.
*/
void flush_workqueue(struct workqueue_struct *wq)
{
@@ -234,28 +236,25 @@ void flush_workqueue(struct workqueue_st
might_sleep();

for (cpu = 0; cpu < NR_CPUS; cpu++) {
+ DEFINE_WAIT(wait);
+ long sequence_needed;
+
if (!cpu_online(cpu))
continue;
cwq = wq->cpu_wq + cpu;

- if (atomic_read(&cwq->nr_queued)) {
- DECLARE_WAITQUEUE(wait, current);
+ spin_lock_irq(&cwq->lock);
+ sequence_needed = cwq->insert_sequence;

- if (!list_empty(&cwq->worklist))
- run_workqueue(cwq);
-
- /*
- * Wait for helper thread(s) to finish up
- * the queue:
- */
- set_current_state(TASK_UNINTERRUPTIBLE);
- add_wait_queue(&cwq->work_done, &wait);
- if (atomic_read(&cwq->nr_queued))
- schedule();
- else
- set_task_state(current, TASK_RUNNING);
- remove_wait_queue(&cwq->work_done, &wait);
+ while (sequence_needed - cwq->remove_sequence > 0) {
+ prepare_to_wait(&cwq->work_done, &wait,
+ TASK_UNINTERRUPTIBLE);
+ spin_unlock_irq(&cwq->lock);
+ schedule();
+ spin_lock_irq(&cwq->lock);
}
+ finish_wait(&cwq->work_done, &wait);
+ spin_unlock_irq(&cwq->lock);
}
}

@@ -281,7 +280,8 @@ struct workqueue_struct *create_workqueu
spin_lock_init(&cwq->lock);
cwq->wq = wq;
cwq->thread = NULL;
- atomic_set(&cwq->nr_queued, 0);
+ cwq->insert_sequence = 0;
+ cwq->remove_sequence = 0;
INIT_LIST_HEAD(&cwq->worklist);
init_waitqueue_head(&cwq->more_work);
init_waitqueue_head(&cwq->work_done);
_

-
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