zfsonlinux/zfs — pull request #490 by Prakash-Surya (2011-12-13 19:27:24+00:00)
Title: Support mutex subclasses in zio_*_child functions

When running ZFS on Linux with CONFIG_LOCK_STAT enabled, lockdep reports
the following warning:

vdev_open/1/8480 is trying to acquire lock:
(&zio->io_lock){+.+...}, at: [] zio_add_child+0x88/0x150 [zfs]

but task is already holding lock:
(&zio->io_lock){+.+...}, at: [] zio_add_child+0x62/0x150 [zfs]

Since this specific lock-chain is valid and nothing to fret about,
lockdep's "nested locking" feature was used to suppress the warning.

Signed-off-by: Prakash Surya
Issue: #488