[PATCH] lockdep: annotate BLKPG_DEL_PARTITION

>=============================================
>[ INFO: possible recursive locking detected ]
>2.6.19-1.2909.fc7 #1
>---------------------------------------------
>anaconda/587 is trying to acquire lock:
> (&bdev->bd_mutex){--..}, at: [<c05fb380>] mutex_lock+0x21/0x24
>
>but task is already holding lock:
> (&bdev->bd_mutex){--..}, at: [<c05fb380>] mutex_lock+0x21/0x24
>
>other info that might help us debug this:
>1 lock held by anaconda/587:
> #0:  (&bdev->bd_mutex){--..}, at: [<c05fb380>] mutex_lock+0x21/0x24
>
>stack backtrace:
> [<c0405812>] show_trace_log_lvl+0x1a/0x2f
> [<c0405db2>] show_trace+0x12/0x14
> [<c0405e36>] dump_stack+0x16/0x18
> [<c043bd84>] __lock_acquire+0x116/0xa09
> [<c043c960>] lock_acquire+0x56/0x6f
> [<c05fb1fa>] __mutex_lock_slowpath+0xe5/0x24a
> [<c05fb380>] mutex_lock+0x21/0x24
> [<c04d82fb>] blkdev_ioctl+0x600/0x76d
> [<c04946b1>] block_ioctl+0x1b/0x1f
> [<c047ed5a>] do_ioctl+0x22/0x68
> [<c047eff2>] vfs_ioctl+0x252/0x265
> [<c047f04e>] sys_ioctl+0x49/0x63
> [<c0404070>] syscall_call+0x7/0xb

Annotate BLKPG_DEL_PARTITION's bd_mutex locking and add a little comment
clarifying the bd_mutex locking, because I confused myself and initially
thought the lock order was wrong too.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/ioctl.c

@@ -82,7 +82,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
 			fsync_bdev(bdevp);
 			invalidate_bdev(bdevp, 0);
 
-			mutex_lock(&bdev->bd_mutex);
+			mutex_lock_nested(&bdev->bd_mutex, 1);
 			delete_partition(disk, part);
 			mutex_unlock(&bdev->bd_mutex);
 			mutex_unlock(&bdevp->bd_mutex);

fs/block_dev.c

@@ -1101,6 +1101,13 @@ static int __blkdev_get(struct block_device *bdev, mode_t mode, unsigned flags,
 			int for_part);
 static int __blkdev_put(struct block_device *bdev, int for_part);
 
+/*
+ * bd_mutex locking:
+ *
+ *  mutex_lock(part->bd_mutex)
+ *    mutex_lock_nested(whole->bd_mutex, 1)
+ */
+
 static int do_open(struct block_device *bdev, struct file *file, int for_part)
 {
 	struct module *owner = NULL;