[dm-devel] [PATCH] dm: Fix lock dependency warning for request based dm
Kiyoshi Ueda
k-ueda at ct.jp.nec.com
Thu Feb 19 03:02:23 UTC 2009
Hi Christof,
On 2009/02/18 23:21 +0900, Christof Schmitt wrote:
> > From: Christof Schmitt <christof.schmitt at de.ibm.com>
> >
> > Testing with request based dm multipathing and lock dependency checking
> > revealed this problem. Fix this by disabling interrupts when acquiring the
> > map_lock from the ioctl call in __bind and __unbind.
> >
> > It seems that the problem has been introduced with this patch:
> > http://lkml.indiana.edu/hypermail/linux/kernel/0810.0/1067.html
Thank you for your testing request-based dm-multipath and the patch.
Attached is a patch to fix it.
Since request-based dm gets map_lock after taking queue_lock with
interrupt disabled, we have to use save/restore variant.
(By the way, although lockdep warns the deadlock possibility, currently
there should be no such code path in request-based dm where request_fn
is called from the interrupt context.)
I have done simple build and boot testings, but haven't done other
testings (e.g. stress testing) yet.
I will include this patch to the next update after such testings.
Thanks,
Kiyoshi Ueda
Index: linux-2.6.29-rc2/drivers/md/dm.c
===================================================================
--- linux-2.6.29-rc2.orig/drivers/md/dm.c
+++ linux-2.6.29-rc2/drivers/md/dm.c
@@ -504,12 +504,13 @@ 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;
}
@@ -1892,6 +1893,7 @@ static int __bind(struct mapped_device *
{
struct request_queue *q = md->queue;
sector_t size;
+ unsigned long flags;
size = dm_table_get_size(t);
@@ -1921,10 +1923,10 @@ static int __bind(struct mapped_device *
if (dm_table_request_based(t) && !blk_queue_stopped(q))
stop_queue(q);
- 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;
}
@@ -1932,14 +1934,15 @@ 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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