The patch titled
Subject: fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4
has been added to the -mm tree. Its filename is
fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4.patch
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------------------------------------------------------
From: Yang Shi <shy828301@xxxxxxxxx>
Subject: fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4
v4: * s/Treated/Treat per David
* Collected acked-by tag from David
v3: * Fixed the fix tag, the one used by v2 was not accurate
* Added comment about the risk calling page_mapcount() per David
* Fix pagemap
Link: https://lkml.kernel.org/r/20220203182641.824731-1-shy828301@xxxxxxxxx
Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()")
Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
Reported-by: syzbot+1f52b3a18d5633fa7f82@xxxxxxxxxxxxxxxxxxxxxxxxx
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/task_mmu.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
--- a/fs/proc/task_mmu.c~fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4
+++ a/fs/proc/task_mmu.c
@@ -469,9 +469,12 @@ static void smaps_account(struct mem_siz
* If any subpage of the compound page mapped with PTE it would elevate
* page_count().
*
- * Treated regular migration entries as mapcount == 1 without reading
- * mapcount since calling page_mapcount() for migration entries is
- * racy against THP splitting.
+ * The page_mapcount() is called to get a snapshot of the mapcount.
+ * Without holding the page lock this snapshot can be slightly wrong as
+ * we cannot always read the mapcount atomically. It is not safe to
+ * call page_mapcount() even with PTL held if the page is not mapped,
+ * especially for migration entries. Treat regular migration entries
+ * as mapcount == 1.
*/
if ((page_count(page) == 1) || migration) {
smaps_page_accumulate(mss, page, size, size << PSS_SHIFT, dirty,
@@ -1393,6 +1396,7 @@ static pagemap_entry_t pte_to_pagemap_en
{
u64 frame = 0, flags = 0;
struct page *page = NULL;
+ bool migration = false;
if (pte_present(pte)) {
if (pm->show_pfn)
@@ -1414,13 +1418,14 @@ static pagemap_entry_t pte_to_pagemap_en
frame = swp_type(entry) |
(swp_offset(entry) << MAX_SWAPFILES_SHIFT);
flags |= PM_SWAP;
+ migration = is_migration_entry(entry);
if (is_pfn_swap_entry(entry))
page = pfn_swap_entry_to_page(entry);
}
if (page && !PageAnon(page))
flags |= PM_FILE;
- if (page && page_mapcount(page) == 1)
+ if (page && !migration && page_mapcount(page) == 1)
flags |= PM_MMAP_EXCLUSIVE;
if (vma->vm_flags & VM_SOFTDIRTY)
flags |= PM_SOFT_DIRTY;
@@ -1436,6 +1441,7 @@ static int pagemap_pmd_range(pmd_t *pmdp
spinlock_t *ptl;
pte_t *pte, *orig_pte;
int err = 0;
+ bool migration = false;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
ptl = pmd_trans_huge_lock(pmdp, vma);
@@ -1476,11 +1482,12 @@ static int pagemap_pmd_range(pmd_t *pmdp
if (pmd_swp_uffd_wp(pmd))
flags |= PM_UFFD_WP;
VM_BUG_ON(!is_pmd_migration_entry(pmd));
+ migration = is_migration_entry(entry);
page = pfn_swap_entry_to_page(entry);
}
#endif
- if (page && page_mapcount(page) == 1)
+ if (page && !migration && page_mapcount(page) == 1)
flags |= PM_MMAP_EXCLUSIVE;
for (; addr != end; addr += PAGE_SIZE) {
_
Patches currently in -mm which might be from shy828301@xxxxxxxxx are
fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry.patch
fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4.patch
