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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 03-18-2009, 07:54 AM
Kiyoshi Ueda
 
Default dm co disable interrupt when taking map_lock

This patch disables interrupt when taking map_lock to prevent
needless lockdep warnings in request-based dm.

request-based dm takes map_lock after taking queue_lock with
disabling interrupt:
spin_lock_irqsave(queue_lock)
q->request_fn() == dm_request_fn()
=> dm_get_table()
=> read_lock(map_lock)
while queue_lock could be taken in interrupt context.

So lockdep warns that a deadlock can happen:
write_lock(map_lock)
<interrupt>
spin_lock_irqsave(queue_lock)
q->request_fn() == dm_request_fn()
=> dm_get_table()
=> read_lock(map_lock)

Currently there is no such code path in request-based dm where
q->request_fn() is called from interrupt context, so no such deadlock
happens.
But such warning messages confuse users, so prevent them by disabling
interrupt when taking map_lock.


Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Christof Schmitt <christof.schmitt@de.ibm.com>
Cc: Alasdair G Kergon <agk@redhat.com>
---
drivers/md/dm.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

Index: 2.6.29-rc8/drivers/md/dm.c
================================================== =================
--- 2.6.29-rc8.orig/drivers/md/dm.c
+++ 2.6.29-rc8/drivers/md/dm.c
@@ -511,12 +511,13 @@ static int queue_io(struct mapped_device
struct dm_table *dm_get_table(struct mapped_device *md)
{
struct dm_table *t;
+ unsigned long flags;

- read_lock(&md->map_lock);
+ read_lock_irqsave(&md->map_lock, flags);
t = md->map;
if (t)
dm_table_get(t);
- read_unlock(&md->map_lock);
+ read_unlock_irqrestore(&md->map_lock, flags);

return t;
}
@@ -1929,6 +1930,7 @@ static int __bind(struct mapped_device *
{
struct request_queue *q = md->queue;
sector_t size;
+ unsigned long flags;

size = dm_table_get_size(t);

@@ -1960,10 +1962,10 @@ static int __bind(struct mapped_device *

__bind_mempools(md, t);

- write_lock(&md->map_lock);
+ write_lock_irqsave(&md->map_lock, flags);
md->map = t;
dm_table_set_restrictions(t, q);
- write_unlock(&md->map_lock);
+ write_unlock_irqrestore(&md->map_lock, flags);

return 0;
}
@@ -1971,14 +1973,15 @@ static int __bind(struct mapped_device *
static void __unbind(struct mapped_device *md)
{
struct dm_table *map = md->map;
+ unsigned long flags;

if (!map)
return;

dm_table_event_callback(map, NULL, NULL);
- write_lock(&md->map_lock);
+ write_lock_irqsave(&md->map_lock, flags);
md->map = NULL;
- write_unlock(&md->map_lock);
+ write_unlock_irqrestore(&md->map_lock, flags);
dm_table_destroy(map);
}


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