On Thu, Jan 18, 2018 at 02:38:39PM +0100, Jan H. Schönherr wrote: > The function follow_pte_pmd() can theoretically return after having > acquired a PMD lock, even when DAX was not compiled with > CONFIG_FS_DAX_PMD. > > Release the PMD lock unconditionally. > > Fixes: f729c8c9b24f ("dax: wrprotect pmd_t in dax_mapping_entry_mkclean") > Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx> > --- > fs/dax.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 9598159..c2ebf10 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -636,8 +636,8 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping, > pmd = pmd_mkclean(pmd); > set_pmd_at(vma->vm_mm, address, pmdp, pmd); > unlock_pmd: > - spin_unlock(ptl); > #endif > + spin_unlock(ptl); > } else { > if (pfn != pte_pfn(*ptep)) > goto unlock_pte; Sure, this seems fine to me. This seems simple and correct - you're right that we aren't taking the PTL on the PMD conditionally based on whether CONFIG_DAX_PMD is defined, so it doesn't make sense to release it conditionally. I think if we ever hit this lock imbalance we're totally insane anyway, but it the fix is correct and doesn't mess with our code flow. You can add: Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>