Re: [PATCH 1/2] xfs: setup VFS i_rwsem lockdep state correctly

[Dave Chinner <david@fromorbit.com>]

On Thu, Jun 07, 2018 at 03:21:31PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> When lockdep is enabled, it changes the type of the inode i_rwsem
> semaphore before unlocking a newly instantiated inode. THere is the
> possibility that there is already a waiter on that inode lock by the
> time we unlock the new inode, so having lockdep re-initialise the
> lock is a vector for trouble.
> 
> Avoid this whole situation by setting up the i_rwsem lockdep class
> at the same time we set up the XFS inode i_ilock classes and so the
> VFS doesn't have to change the lock class itself when it is
> potentially unsafe.
> 
> Signed-Off-By: Dave Chinner <dchinner@redhat.com>

I just realised that the VFS equivalent patch has made it upstream,
too, which would help explain this a bit more. Darrick, can you add
this to the commit message:

"This change is necessary because the equivalent fixes to the VFS
code made in commit 1e2e547a93a0 ("do d_instantiate/unlock_new_inode
combinations safely") are not relevant to XFS as it has it's own
internal inode cache lookup and instantiation routines."

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com