From: Hugh Dickins <hughd@xxxxxxxxxx> commit f2b277c4d1c63a85127e8aa2588e9cc3bd21cb99 upstream. Wangyong reports: after enabling tmpfs filesystem to support transparent hugepage with the following command: echo always > /sys/kernel/mm/transparent_hugepage/shmem_enabled the docker program tries to add F_SEAL_WRITE through the following command, but it fails unexpectedly with errno EBUSY: fcntl(5, F_ADD_SEALS, F_SEAL_WRITE) = -1. That is because memfd_tag_pins() and memfd_wait_for_pins() were never updated for shmem huge pages: checking page_mapcount() against page_count() is hopeless on THP subpages - they need to check total_mapcount() against page_count() on THP heads only. Make memfd_tag_pins() (compared > 1) as strict as memfd_wait_for_pins() (compared != 1): either can be justified, but given the non-atomic total_mapcount() calculation, it is better now to be strict. Bear in mind that total_mapcount() itself scans all of the THP subpages, when choosing to take an XA_CHECK_SCHED latency break. Also fix the unlikely xa_is_value() case in memfd_wait_for_pins(): if a page has been swapped out since memfd_tag_pins(), then its refcount must have fallen, and so it can safely be untagged. Link: https://lkml.kernel.org/r/a4f79248-df75-2c8c-3df-ba3317ccb5da@xxxxxxxxxx Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Reported-by: Zeal Robot <zealci@xxxxxxxxxx> Reported-by: wangyong <wang.yong12@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: CGEL ZTE <cgel.zte@xxxxxxxxx> Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Yang Yang <yang.yang29@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2478,7 +2478,8 @@ static void shmem_tag_pins(struct addres slot = radix_tree_iter_retry(&iter); continue; } - } else if (page_count(page) - page_mapcount(page) > 1) { + } else if (!PageTail(page) && page_count(page) != + hpage_nr_pages(page) + total_mapcount(page)) { radix_tree_tag_set(&mapping->page_tree, iter.index, SHMEM_TAG_PINNED); } @@ -2538,8 +2539,8 @@ static int shmem_wait_for_pins(struct ad page = NULL; } - if (page && - page_count(page) - page_mapcount(page) != 1) { + if (page && page_count(page) != + hpage_nr_pages(page) + total_mapcount(page)) { if (scan < LAST_SCAN) goto continue_resched;
