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bcache: do not mark writeback_running too early

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A fresh backing device is not attached to any cache_set, and
has no writeback kthread created until first attached to some
cache_set.

But bch_cached_dev_writeback_init run
"
	dc->writeback_running		= true;
	WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING,
			&dc->disk.flags));
"
for any newly formatted backing devices.

For a fresh standalone backing device, we can get something like
following even if no writeback kthread created:
------------------------
/sys/block/bcache0/bcache# cat writeback_running
1
/sys/block/bcache0/bcache# cat writeback_rate_debug
rate:		512.0k/sec
dirty:		0.0k
target:		0.0k
proportional:	0.0k
integral:	0.0k
change:		0.0k/sec
next io:	-15427384ms

The none ZERO fields are misleading as no alive writeback kthread yet.

Set dc->writeback_running false as no writeback thread created in
bch_cached_dev_writeback_init().

We have writeback thread created and woken up in bch_cached_dev_writeback
_start(). Set dc->writeback_running true before bch_writeback_queue()
called, as a writeback thread will check if dc->writeback_running is true
before writing back dirty data, and hung if false detected.

After the change, we can get the following output for a fresh standalone
backing device:
-----------------------
/sys/block/bcache0/bcache$ cat writeback_running
0
/sys/block/bcache0/bcache# cat writeback_rate_debug
rate:		0.0k/sec
dirty:		0.0k
target:		0.0k
proportional:	0.0k
integral:	0.0k
change:		0.0k/sec
next io:	0ms

v1 -> v2:
  Set dc->writeback_running before bch_writeback_queue() called,

Signed-off-by: Shenghui Wang <shhuiw@foxmail.com>
Signed-off-by: Coly Li <colyli@suse.de>

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Shenghui Wang 2018-12-13 22:53:50 +08:00 committed by Jens Axboe
parent 4e361e020e
commit 79b791466e
1 changed files with 2 additions and 1 deletions
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3
drivers/md/bcache/writeback.c
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@ -777,7 +777,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
bch_keybuf_init(&dc->writeback_keys);
dc->writeback_metadata = true;
dc->writeback_running = true;
dc->writeback_running = false;
dc->writeback_percent = 10;
dc->writeback_delay = 30;
atomic_long_set(&dc->writeback_rate.rate, 1024);
@ -805,6 +805,7 @@ int bch_cached_dev_writeback_start(struct cached_dev *dc)
cached_dev_put(dc);
return PTR_ERR(dc->writeback_thread);
}
dc->writeback_running = true;
WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
schedule_delayed_work(&dc->writeback_rate_update,