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bcache: Avoid hung task happen.

PATCH In review majianpeng 2 participants 3 messages Jan 8, 2014 – Jan 9, 2014 bcache (block layer cache)

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majianpeng

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#0 lore raw

PATCH 2/3 bcache: Avoid hung task happen.

Because after kthread_create, the state of kthread is TASK_UNINTERRUPTIBLE. If we don't wake up dc->writeback_thread, the thread will be hung-task. For those reasons, we don't wake up writeback_thread:
A:only create backed device
B:create backed device and cache device, but don't write at once C:write without writeback poliy

So like the way of create gc_thread, after creating writeback_thread, i set the state is TASK_INTERRUPTIBLE.

Signed-off-by Jianpeng Ma <[email protected]>
---
 drivers/md/bcache/writeback.c |    2 ++
 1 file changed, 2 insertions(+)
drivers/md/bcache/writeback.c +2 -0
index 6c44fe0..7fbc22a 100644
@@ -499,6 +499,8 @@ int bch_cached_dev_writeback_init(struct cached_dev *dc)
 	if (IS_ERR(dc->writeback_thread))
 		return PTR_ERR(dc->writeback_thread);
 
+	set_task_state(dc->writeback_thread, TASK_INTERRUPTIBLE);
+
 	INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
 	schedule_delayed_work(&dc->writeback_rate_update,
 			      dc->writeback_rate_update_seconds * HZ);
Signature · 1 line
1.7.10.4
#1 lore raw
Quoted 9 lines · majianpeng

Because after kthread_create, the state of kthread is TASK_UNINTERRUPTIBLE. If we don't wake up dc->writeback_thread, the thread will be hung-task. For those reasons, we don't wake up writeback_thread:
A:only create backed device
B:create backed device and cache device, but don't write at once C:write without writeback poliy

So like the way of create gc_thread, after creating writeback_thread, i set the state is TASK_INTERRUPTIBLE.

I've seen this issue, but this isn't even where the sleep happens, there's no way this could be fixing it..

author
#2 lore raw
Quoted 8 lines · majianpeng
Quoted 7 lines

Because after kthread_create, the state of kthread is TASK_UNINTERRUPTIBLE. If we don't wake up dc->writeback_thread, the thread will be hung-task. For those reasons, we don't wake up writeback_thread:
A:only create backed device
B:create backed device and cache device, but don't write at once C:write without writeback poliy

Quoted 5 lines
Quoted 2 lines

So like the way of create gc_thread, after creating writeback_thread, i set the state is TASK_INTERRUPTIBLE.

I've seen this issue, but this isn't even where the sleep happens, there's no way this could be fixing it..

Yes.But now, the default cache mode is writethrough.So kernel also printk hung-task messages. If you don't like this way, you can use kthread_run instead kthread_create. Because you test dc->has_dirty in bch_writeback_thread,so using kthread_run is safe.

Thanks!
Jianpeng Ma