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.
Reported-by: Zeal Robot <zealci@xxxxxxxxxx>
Reported-by: wangyong <wang.yong12@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
Andrew, please remove
fix-shmem-huge-page-failed-to-set-f_seal_write-attribute-problem.patch
fix-shmem-huge-page-failed-to-set-f_seal_write-attribute-problem-fix.patch
from mmotm, and replace them by this patch against 5.17-rc5:
wangyong's patch did not handle the case of pte-mapped huge pages, and I
had this one from earlier, when I found the same issue with MFD_HUGEPAGE
(but MFD_HUGEPAGE did not go in, so I didn't post this one, forgetting
the transparent_hugepage/shmem_enabled case).
mm/memfd.c | 40 ++++++++++++++++++++++++++++------------
1 file changed, 28 insertions(+), 12 deletions(-)
--- 5.17-rc5/mm/memfd.c
+++ linux/mm/memfd.c
@@ -31,20 +31,28 @@
static void memfd_tag_pins(struct xa_state *xas)
{
struct page *page;
- unsigned int tagged = 0;
+ int latency = 0;
+ int cache_count;
lru_add_drain();
xas_lock_irq(xas);
xas_for_each(xas, page, ULONG_MAX) {
- if (xa_is_value(page))
- continue;
- page = find_subpage(page, xas->xa_index);
- if (page_count(page) - page_mapcount(page) > 1)
+ cache_count = 1;
+ if (!xa_is_value(page) &&
+ PageTransHuge(page) && !PageHuge(page))
+ cache_count = HPAGE_PMD_NR;
+
+ if (!xa_is_value(page) &&
+ page_count(page) - total_mapcount(page) != cache_count)
xas_set_mark(xas, MEMFD_TAG_PINNED);
+ if (cache_count != 1)
+ xas_set(xas, page->index + cache_count);
- if (++tagged % XA_CHECK_SCHED)
+ latency += cache_count;
+ if (latency < XA_CHECK_SCHED)
continue;
+ latency = 0;
xas_pause(xas);
xas_unlock_irq(xas);
@@ -73,7 +81,8 @@ static int memfd_wait_for_pins(struct ad
error = 0;
for (scan = 0; scan <= LAST_SCAN; scan++) {
- unsigned int tagged = 0;
+ int latency = 0;
+ int cache_count;
if (!xas_marked(&xas, MEMFD_TAG_PINNED))
break;
@@ -87,10 +96,14 @@ static int memfd_wait_for_pins(struct ad
xas_lock_irq(&xas);
xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
- if (xa_is_value(page))
- continue;
- page = find_subpage(page, xas.xa_index);
- if (page_count(page) - page_mapcount(page) != 1) {
+
+ cache_count = 1;
+ if (!xa_is_value(page) &&
+ PageTransHuge(page) && !PageHuge(page))
+ cache_count = HPAGE_PMD_NR;
+
+ if (!xa_is_value(page) && cache_count !=
+ page_count(page) - total_mapcount(page)) {
/*
* On the last scan, we clean up all those tags
* we inserted; but make a note that we still
@@ -103,8 +116,11 @@ static int memfd_wait_for_pins(struct ad
}
if (clear)
xas_clear_mark(&xas, MEMFD_TAG_PINNED);
- if (++tagged % XA_CHECK_SCHED)
+
+ latency += cache_count;
+ if (latency < XA_CHECK_SCHED)
continue;
+ latency = 0;
xas_pause(&xas);
xas_unlock_irq(&xas);
