From: Jens Axboe <axboe@suse.de>
At SUSE I reproduced a problem with dm and ide disks on a 4-way where ide
request_fn would discover the queue plugged all of a sudden, and then give
up on doing io. The problem is due to the fact that dm now sets
QUEUE_FLAG_PLUGGED without holding the target queue lock. I think the best
fix is simply not to set the PLUGGED bit outside of the queue lock, and
just let __generic_unplug_device() always call down into the request_fn()
even if the queue wasn't plugged. This should be a very rare occurence.
---
25-akpm/drivers/block/ll_rw_blk.c | 7 +++++--
25-akpm/drivers/md/dm-table.c | 4 +---
2 files changed, 6 insertions(+), 5 deletions(-)
diff -puN drivers/block/ll_rw_blk.c~per-backing_dev-unplugging-dm-fix drivers/block/ll_rw_blk.c
--- 25/drivers/block/ll_rw_blk.c~per-backing_dev-unplugging-dm-fix 2004-03-16 13:17:49.754333688 -0800
+++ 25-akpm/drivers/block/ll_rw_blk.c 2004-03-16 13:17:49.760332776 -0800
@@ -1134,8 +1134,11 @@ static inline void __generic_unplug_devi
if (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags))
return;
- if (!blk_remove_plug(q))
- return;
+ /*
+ * always call down, since we can race now with setting the plugged
+ * bit outside of the queue lock
+ */
+ (void) blk_remove_plug(q);
/*
* was plugged, fire request_fn if queue has stuff to do
diff -puN drivers/md/dm-table.c~per-backing_dev-unplugging-dm-fix drivers/md/dm-table.c
--- 25/drivers/md/dm-table.c~per-backing_dev-unplugging-dm-fix 2004-03-16 13:17:49.755333536 -0800
+++ 25-akpm/drivers/md/dm-table.c 2004-03-16 13:17:49.761332624 -0800
@@ -893,10 +893,8 @@ void dm_table_unplug_all(struct dm_table
struct dm_dev *dd = list_entry(d, struct dm_dev, list);
request_queue_t *q = bdev_get_queue(dd->bdev);
- if (q->unplug_fn) {
- set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
+ if (q->unplug_fn)
q->unplug_fn(q);
- }
}
}
_