On Tue, Jul 30, 2013 at 04:46:00PM +0200, Michal Hocko wrote: > which is a false positive caused by hugetlb pmd sharing code which > allocates a new pmd from withing mappint->i_mmap_mutex. If this > allocation causes reclaim then the lockdep detector complains that we > might self-deadlock. > > This is not correct though, because hugetlb pages are not reclaimable so > their mapping will be never touched from the reclaim path. > > The patch tells lockup detector that hugetlb i_mmap_mutex is special > by assigning it a separate lockdep class so it won't report possible > deadlocks on unrelated mappings. > > Reported-by: Dave Jones <davej@xxxxxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > --- > fs/hugetlbfs/inode.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index a3f868a..230533d 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -463,6 +463,12 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb, > return inode; > } > > +/* > + * Now, reclaim path never holds hugetlbfs_inode->i_mmap_mutex while it could > + * hold normal inode->i_mmap_mutex so this annotation avoids a lockdep splat. How about something like: /* * Hugetlbfs is not reclaimable; therefore its i_mmap_mutex will never * be taken from reclaim -- unlike regular filesystems. This needs an * annotation because huge_pmd_share() does an allocation under * i_mmap_mutex. */ It clarifies the exact conditions and makes easier to verify the validity of the annotation. > + */ > +struct lock_class_key hugetlbfs_i_mmap_mutex_key; > + > static struct inode *hugetlbfs_get_inode(struct super_block *sb, > struct inode *dir, > umode_t mode, dev_t dev) > @@ -474,6 +480,8 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb, > struct hugetlbfs_inode_info *info; > inode->i_ino = get_next_ino(); > inode_init_owner(inode, dir, mode); > + lockdep_set_class(&inode->i_mapping->i_mmap_mutex, > + &hugetlbfs_i_mmap_mutex_key); > inode->i_mapping->a_ops = &hugetlbfs_aops; > inode->i_mapping->backing_dev_info =&hugetlbfs_backing_dev_info; > inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; > -- > 1.8.3.2 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>