On Wed, 2017-12-13 at 09:20 -0500, Jeff Layton wrote: > From: Jeff Layton <jlayton@xxxxxxxxxx> > > The rationale for taking the i_lock when incrementing this value is > lost in antiquity. The readers of the field don't take it (at least > not universally), so my assumption is that it was only done here to > serialize incrementors. > > If that is indeed the case, then we can drop the i_lock from this > codepath and treat it as a atomic64_t for the purposes of > incrementing it. This allows us to use inode_inc_iversion without > any danger of lock inversion. > > Note that the read side is not fetched atomically with this change. > The assumption here is that that is not a critical issue since the > i_version is not fully synchronized with anything else anyway. > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > --- > include/linux/fs.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 5001e77342fd..c234fac4bb77 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2136,9 +2136,9 @@ inode_set_iversion_queried(struct inode *inode, const u64 new) > static inline bool > inode_maybe_inc_iversion(struct inode *inode, bool force) > { > - spin_lock(&inode->i_lock); > - inode->i_version++; > - spin_unlock(&inode->i_lock); > + atomic64_t *ivp = (atomic64_t *)&inode->i_version; > + > + atomic64_inc(ivp); > return true; > } > FWIW, I'm not sure this patch is strictly necessary as an interim step. Adding the i_lock into the all of the places where we currently just do inode->i_version++ without properly auditing all of them gave me pause though. In any case, the last patch in the series cleans this nastiness up. -- Jeff Layton <jlayton@xxxxxxxxxx>