jffs2: fix lockdep warning

This patch series essentially fixes a false positive lockdep warning. The issue is known since 2012, referenced and fixed in the third patch. The other two patches subtly change the locking semantics on order to make the third patch feasible.

I would like thank Peter Zijlstra for his precise guiding on where to look. His first guess on what is going nailed it. I would also like to thank David Woodhouse and Richard Weinberger for their reviews.

Changes in v3:
- Avoid ?: operator (requested by Richard Weinberger).
- Add Reviewed-by tags from Richard Weinberger.
- Rebase patch series on v4.20-rc7.
- Update my email address.

Changes in v2:
- Initialize the lock class on every inode initialization rather than just the initial one in jffs2_i_init_once. (Thanks to David Woodhouse for pointing at this issue.)
- Properly wrap the commit message to make checkpatch.pl fully happy.

Helmut Grohne (3):
jffs2: avoid unnecessarily taking f->sem
jffs2: jffs2_iget defer f->sem acquisition
jffs2: put directories f->sem on a separate lockdep class

 fs/jffs2/fs.c        | 21 ++++++++++++++++++++-
 fs/jffs2/readinode.c |  4 +---
 2 files changed, 21 insertions(+), 4 deletions(-)

2.11.0