lkml.org 
[lkml]   [2022]   [Mar]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.19 48/51] memfd: fix F_SEAL_WRITE after shmem huge page allocated
Date
From: Hugh Dickins <hughd@google.com>

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@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Reported-by: wangyong <wang.yong12@zte.com.cn>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: CGEL ZTE <cgel.zte@gmail.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/memfd.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)

--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -34,26 +34,35 @@ static void memfd_tag_pins(struct addres
void __rcu **slot;
pgoff_t start;
struct page *page;
- unsigned int tagged = 0;
+ int latency = 0;
+ int cache_count;

lru_add_drain();
start = 0;

xa_lock_irq(&mapping->i_pages);
radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
+ cache_count = 1;
page = radix_tree_deref_slot_protected(slot, &mapping->i_pages.xa_lock);
- if (!page || radix_tree_exception(page)) {
+ if (!page || radix_tree_exception(page) || PageTail(page)) {
if (radix_tree_deref_retry(page)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
- } else if (page_count(page) - page_mapcount(page) > 1) {
- radix_tree_tag_set(&mapping->i_pages, iter.index,
- MEMFD_TAG_PINNED);
+ } else {
+ if (PageTransHuge(page) && !PageHuge(page))
+ cache_count = HPAGE_PMD_NR;
+ if (cache_count !=
+ page_count(page) - total_mapcount(page)) {
+ radix_tree_tag_set(&mapping->i_pages,
+ iter.index, MEMFD_TAG_PINNED);
+ }
}

- if (++tagged % 1024)
+ latency += cache_count;
+ if (latency < 1024)
continue;
+ latency = 0;

slot = radix_tree_iter_resume(slot, &iter);
xa_unlock_irq(&mapping->i_pages);
@@ -79,6 +88,7 @@ static int memfd_wait_for_pins(struct ad
pgoff_t start;
struct page *page;
int error, scan;
+ int cache_count;

memfd_tag_pins(mapping);

@@ -107,8 +117,12 @@ static int memfd_wait_for_pins(struct ad
page = NULL;
}

- if (page &&
- page_count(page) - page_mapcount(page) != 1) {
+ cache_count = 1;
+ if (page && PageTransHuge(page) && !PageHuge(page))
+ cache_count = HPAGE_PMD_NR;
+
+ if (page && cache_count !=
+ page_count(page) - total_mapcount(page)) {
if (scan < LAST_SCAN)
goto continue_resched;


\
 
 \ /
  Last update: 2022-03-07 10:35    [W:0.193 / U:0.336 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site