[PATCH 004 of 4] Avoid lockdep warning in md.

NeilBrown
2006-10-11T06:09:53Z

md_open takes ->reconfig_mutex which causes lockdep to complain.
This (normally) doesn't have deadlock potential as the possible
conflict is with a reconfig_mutex in a different device.

I say "normally" because if a loop were created in the array->member
hierarchy a deadlock could happen. However that causes bigger
problems than a deadlock and should be fixed independently.

So we flag the lock in md_open as a nested lock. This requires
defining mutex_lock_interruptible_nested.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/md.c | 2 +-
./include/linux/mutex.h | 2 ++
./kernel/mutex.c | 9 +++++++++
3 files changed, 12 insertions(+), 1 deletion(-)

diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c 2006-10-11 15:53:48.000000000 +1000
+++ ./drivers/md/md.c 2006-10-11 15:42:09.000000000 +1000
@@ -4422,7 +4422,7 @@ static int md_open(struct inode *inode,
mddev_t *mddev = inode->i_bdev->bd_disk->private_data;
int err;

- if ((err = mddev_lock(mddev)))
+ if ((err = mutex_lock_interruptible_nested(&mddev->reconfig_mutex, 1)))
goto out;

err = 0;

diff .prev/include/linux/mutex.h ./include/linux/mutex.h
--- .prev/include/linux/mutex.h 2006-10-11 15:53:48.000000000 +1000
+++ ./include/linux/mutex.h 2006-10-11 15:43:22.000000000 +1000
@@ -125,8 +125,10 @@ extern int fastcall mutex_lock_interrupt

#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
+extern int mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass);
#else
# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
+# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
#endif

/*

diff .prev/kernel/mutex.c ./kernel/mutex.c
--- .prev/kernel/mutex.c 2006-10-11 15:53:48.000000000 +1000
+++ ./kernel/mutex.c 2006-10-11 15:45:08.000000000 +1000
@@ -206,6 +206,15 @@ mutex_lock_nested(struct mutex *lock, un
}

EXPORT_SYMBOL_GPL(mutex_lock_nested);
+
+int __sched
+mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
+{
+ might_sleep();
+ return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass);
+}
+
+EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
#endif

/*