Hi Michal, On Thu, Jul 25, 2013 at 03:30:40PM +0200, Michal Hocko wrote: > On Wed 24-07-13 11:44:28, Minchan Kim wrote: > > On Tue, Jul 23, 2013 at 04:01:20PM +0200, Michal Hocko wrote: > > > On Fri 19-07-13 09:13:03, Minchan Kim wrote: > > > > On Thu, Jul 18, 2013 at 11:12:24PM +0530, Aneesh Kumar K.V wrote: > > > [...] > > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > > > > index 83aff0a..2cb1be3 100644 > > > > > --- a/mm/hugetlb.c > > > > > +++ b/mm/hugetlb.c > > > > > @@ -3266,8 +3266,8 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > > > > > put_page(virt_to_page(spte)); > > > > > spin_unlock(&mm->page_table_lock); > > > > > out: > > > > > - pte = (pte_t *)pmd_alloc(mm, pud, addr); > > > > > mutex_unlock(&mapping->i_mmap_mutex); > > > > > + pte = (pte_t *)pmd_alloc(mm, pud, addr); > > > > > return pte; > > > > > > > > I am blind on hugetlb but not sure it doesn't break eb48c071. > > > > Michal? > > > > > > Well, it is some time since I debugged the race and all the details > > > vanished in the meantime. But this part of the changelog suggests that > > > this indeed breaks the fix: > > > " > > > This patch addresses the issue by moving pmd_alloc into huge_pmd_share > > > which guarantees that the shared pud is populated in the same critical > > > section as pmd. This also means that huge_pte_offset test in > > > huge_pmd_share is serialized correctly now which in turn means that the > > > success of the sharing will be higher as the racing tasks see the pud > > > and pmd populated together. > > > " > > > > > > Besides that I fail to see how moving pmd_alloc down changes anything. > > > Even if pmd_alloc triggered reclaim then we cannot trip over the same > > > i_mmap_mutex as hugetlb pages are not reclaimable because they are not > > > on the LRU. > > > > I thought we could map some part of binary with normal page and other part > > of the one with MAP_HUGETLB so that a address space could have both normal > > page and HugeTLB page. Okay, it's impossible so HugeTLB pages are not on LRU. > > Then, above lockdep warning is totally false positive. > > Best solution is avoiding pmd_alloc with holding i_mmap_mutex but we need it > > to fix eb48c071 so how about this if we couldn't have a better idea? > > Shouldn't we rather use a hugetlb specific lock_class_key. I am not > familiar with lockdep much but something like bellow should do the > trick? Looks good to me. Could you resend it with formal patch with Ccing Peter for Dave to confirm it? Below just a nitpick. > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index a3f868a..40a61f6 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -463,6 +463,8 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb, > return inode; > } > > +struct lock_class_key hugetlbfs_i_mmap_mutex_key; Let's add comment why we need this special something. How about this? /* * Now, reclaim path never hold hugetlbfs_inode->i_mmap_mutex while it could * hold normal inode->i_mmap_mutex so this annoation avoids a lockdep splat. */ static struct lock_class_key hugetlbctx_mutex; > + > static struct inode *hugetlbfs_get_inode(struct super_block *sb, > struct inode *dir, > umode_t mode, dev_t dev) > @@ -474,6 +476,7 @@ 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; > -- > Michal Hocko > SUSE Labs > > -- > 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> -- Kind regards, Minchan Kim -- 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>