On 9/3/2024 9:06 PM, Kasireddy, Vivek wrote:
Hi Steve,
Subject: [PATCH V1 4/5] mm/gup: fix memfd_pin_folios hugetlb page
allocation
When memfd_pin_folios -> memfd_alloc_folio creates a hugetlb page, the
index is wrong. The subsequent call to filemap_get_folios_contig thus
cannot find it, and fails, and memfd_pin_folios loops forever.
To fix, adjust the index for the huge_page_order.
memfd_alloc_folio also forgets to unlock the folio, so the next touch
of the page calls hugetlb_fault which blocks forever trying to take
the lock. Unlock it.
Where exactly is the lock taken from? I did a quick search but couldn't
immediately figure out in which function is the lock taken, while allocating
the folio.
memfd_alloc_folio -> hugetlb_add_to_page_cache -> __folio_set_locked
I forgot to add that detail to the commit message.
See for example hugetlbfs_fallocate which calls hugetlb_add_to_page_cache and
then calls folio_unlock before returning.
- Steve
Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning
memfd folios")
Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
---
mm/memfd.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/memfd.c b/mm/memfd.c
index bfe0e71..bcb131d 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -79,10 +79,13 @@ struct folio *memfd_alloc_folio(struct file *memfd,
pgoff_t idx)
* alloc from. Also, the folio will be pinned for an indefinite
* amount of time, so it is not expected to be migrated away.
*/
- gfp_mask = htlb_alloc_mask(hstate_file(memfd));
+ struct hstate *h = hstate_file(memfd);
+
+ gfp_mask = htlb_alloc_mask(h);
gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
+ idx >>= huge_page_order(h);
- folio = alloc_hugetlb_folio_reserve(hstate_file(memfd),
+ folio = alloc_hugetlb_folio_reserve(h,
numa_node_id(),
NULL,
gfp_mask);
@@ -95,6 +98,7 @@ struct folio *memfd_alloc_folio(struct file *memfd,
pgoff_t idx)
free_huge_folio(folio);
return ERR_PTR(err);
}
+ folio_unlock(folio);
Acked-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
Thanks,
Vivek
return folio;
}
return ERR_PTR(-ENOMEM);
--
1.8.3.1
