On Thu, 12 Jul 2012, Mike Galbraith wrote:
> On Thu, 2012-07-12 at 13:43 +0200, Thomas Gleixner wrote:
> > rawlock points to ...968 and the node_list to ...970.
> >
> > struct rt_mutex {
> > raw_spinlock_t wait_lock;
> > struct plist_head wait_list;
> >
> > The raw_lock pointer of the plist_head is initialized in
> > __rt_mutex_init() so it points to wait_lock.
> >
> > Can you check the offset of wait_list vs. the rt_mutex itself?
> >
> > I wouldn't be surprised if it's exactly 8 bytes. And then this thing
> > looks like a copied lock with stale pointers to hell. Eew.
>
> crash> struct rt_mutex -o
> struct rt_mutex {
> [0] raw_spinlock_t wait_lock;
> [8] struct plist_head wait_list;
Bingo, that makes it more likely that this is caused by copying w/o
initializing the lock and then freeing the original structure.
A quick check for memcpy finds that __btrfs_close_devices() does a
memcpy of btrfs_device structs w/o initializing the lock in the new
copy, but I have no idea whether that's the place we are looking for.
Thanks,
tglx
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 43baaf0..06c8ced 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -512,6 +512,7 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
new_device->writeable = 0;
new_device->in_fs_metadata = 0;
new_device->can_discard = 0;
+ spin_lock_init(&new_device->io_lock);
list_replace_rcu(&device->dev_list, &new_device->dev_list);
call_rcu(&device->rcu, free_device);
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