The quilt patch titled
Subject: mm/userfaultfd: retry if pte_offset_map() fails
has been removed from the -mm tree. Its filename was
mm-userfaultfd-retry-if-pte_offset_map-fails.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/userfaultfd: retry if pte_offset_map() fails
Date: Thu, 8 Jun 2023 18:24:38 -0700 (PDT)
Instead of worrying whether the pmd is stable, userfaultfd_must_wait()
call pte_offset_map() as before, but go back to try again if that fails.
Risk of endless loop? It already broke out if pmd_none(), !pmd_present()
or pmd_trans_huge(), and pte_offset_map() would have cleared pmd_bad():
which leaves pmd_devmap(). Presumably pmd_devmap() is inappropriate in a
vma subject to userfaultfd (it would have been mistreated before), but add
a check just to avoid all possibility of endless loop there.
Link: https://lkml.kernel.org/r/54423f-3dff-fd8d-614a-632727cc4cfb@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Steven Price <steven.price@xxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Zack Rusin <zackr@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/fs/userfaultfd.c~mm-userfaultfd-retry-if-pte_offset_map-fails
+++ a/fs/userfaultfd.c
@@ -349,12 +349,13 @@ static inline bool userfaultfd_must_wait
if (!pud_present(*pud))
goto out;
pmd = pmd_offset(pud, address);
+again:
_pmd = pmdp_get_lockless(pmd);
if (pmd_none(_pmd))
goto out;
ret = false;
- if (!pmd_present(_pmd))
+ if (!pmd_present(_pmd) || pmd_devmap(_pmd))
goto out;
if (pmd_trans_huge(_pmd)) {
@@ -363,11 +364,11 @@ static inline bool userfaultfd_must_wait
goto out;
}
- /*
- * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
- * and use the standard pte_offset_map() instead of parsing _pmd.
- */
pte = pte_offset_map(pmd, address);
+ if (!pte) {
+ ret = true;
+ goto again;
+ }
/*
* Lockless access: we're in a wait_event so it's ok if it
* changes under us. PTE markers should be handled the same as none
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
