From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <shy828301@gmail.com>,
Wang Yugui <wangyugui@e16-tech.com>,
Matthew Wilcox <willy@infradead.org>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>, Zi Yan <ziy@nvidia.com>,
Peter Xu <peterx@redhat.com>, Will Deacon <will@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH 10/11] mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes
Date: Wed, 9 Jun 2021 23:52:37 -0700 (PDT) [thread overview]
Message-ID: <fedb8632-1798-de42-f39e-873551d5bc81@google.com> (raw)
In-Reply-To: <589b358c-febc-c88e-d4c2-7834b37fa7bf@google.com>
Running certain tests with a DEBUG_VM kernel would crash within hours,
on the total_mapcount BUG() in split_huge_page_to_list(), while trying
to free up some memory by punching a hole in a shmem huge page: split's
try_to_unmap() was unable to find all the mappings of the page (which,
on a !DEBUG_VM kernel, would then keep the huge page pinned in memory).
Crash dumps showed two tail pages of a shmem huge page remained mapped
by pte: ptes in a non-huge-aligned vma of a gVisor process, at the end
of a long unmapped range; and no page table had yet been allocated for
the head of the huge page to be mapped into.
Although designed to handle these odd misaligned huge-page-mapped-by-pte
cases, page_vma_mapped_walk() falls short by returning false prematurely
when !pmd_present or !pud_present or !p4d_present or !pgd_present: there
are cases when a huge page may span the boundary, with ptes present in
the next.
Restructure page_vma_mapped_walk() as a loop to continue in these cases,
while keeping its layout much as before. Add a step_forward() helper to
advance pvmw->address across those boundaries: originally I tried to use
mm's standard p?d_addr_end() macros, but hit the same crash 512 times
less often: because of the way redundant levels are folded together,
but folded differently in different configurations, it was just too
difficult to use them correctly; and step_forward() is simpler anyway.
Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
---
mm/page_vma_mapped.c | 34 +++++++++++++++++++++++++---------
1 file changed, 25 insertions(+), 9 deletions(-)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index f6839f536645..6eb2f1863506 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -116,6 +116,13 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
return pfn_is_match(pvmw->page, pfn);
}
+static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
+{
+ pvmw->address = (pvmw->address + size) & ~(size - 1);
+ if (!pvmw->address)
+ pvmw->address = ULONG_MAX;
+}
+
/**
* page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
* @pvmw->address
@@ -183,16 +190,22 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (pvmw->pte)
goto next_pte;
restart:
- {
+ do {
pgd = pgd_offset(mm, pvmw->address);
- if (!pgd_present(*pgd))
- return false;
+ if (!pgd_present(*pgd)) {
+ step_forward(pvmw, PGDIR_SIZE);
+ continue;
+ }
p4d = p4d_offset(pgd, pvmw->address);
- if (!p4d_present(*p4d))
- return false;
+ if (!p4d_present(*p4d)) {
+ step_forward(pvmw, P4D_SIZE);
+ continue;
+ }
pud = pud_offset(p4d, pvmw->address);
- if (!pud_present(*pud))
- return false;
+ if (!pud_present(*pud)) {
+ step_forward(pvmw, PUD_SIZE);
+ continue;
+ }
pvmw->pmd = pmd_offset(pud, pvmw->address);
/*
@@ -240,7 +253,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
spin_unlock(ptl);
}
- return false;
+ step_forward(pvmw, PMD_SIZE);
+ continue;
}
if (!map_pte(pvmw))
goto next_pte;
@@ -270,7 +284,9 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
spin_lock(pvmw->ptl);
}
goto this_pte;
- }
+ } while (pvmw->address < end);
+
+ return false;
}
/**
--
2.26.2
next prev parent reply other threads:[~2021-06-10 6:53 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 6:31 [PATCH 00/11] mm: page_vma_mapped_walk() cleanup and THP fixes Hugh Dickins
2021-06-10 6:34 ` [PATCH 01/11] mm: page_vma_mapped_walk(): use page for pvmw->page Hugh Dickins
2021-06-10 8:12 ` Alistair Popple
2021-06-10 8:55 ` Kirill A. Shutemov
2021-06-10 14:14 ` Peter Xu
2021-06-10 22:35 ` Hugh Dickins
2021-06-10 6:36 ` [PATCH 02/11] mm: page_vma_mapped_walk(): settle PageHuge on entry Hugh Dickins
2021-06-10 8:57 ` Kirill A. Shutemov
2021-06-10 14:17 ` Peter Xu
2021-06-10 22:45 ` Hugh Dickins
2021-06-10 6:38 ` [PATCH 03/11] mm: page_vma_mapped_walk(): use pmd_read_atomic() Hugh Dickins
2021-06-10 9:06 ` Kirill A. Shutemov
2021-06-10 12:15 ` Jason Gunthorpe
2021-06-11 6:37 ` Hugh Dickins
2021-06-11 15:36 ` Jason Gunthorpe
2021-06-11 19:05 ` Hugh Dickins
2021-06-11 19:42 ` Jason Gunthorpe
2021-06-15 9:46 ` Will Deacon
2021-06-16 0:42 ` Jason Gunthorpe
2021-06-16 10:27 ` Will Deacon
2021-06-11 19:33 ` Hugh Dickins
2021-06-10 6:40 ` [PATCH 04/11] mm: page_vma_mapped_walk(): use pmde for *pvmw->pmd Hugh Dickins
2021-06-10 9:10 ` Kirill A. Shutemov
2021-06-10 14:31 ` Peter Xu
2021-06-10 6:42 ` [PATCH 05/11] mm: page_vma_mapped_walk(): prettify PVMW_MIGRATION block Hugh Dickins
2021-06-10 9:16 ` Kirill A. Shutemov
2021-06-10 14:48 ` Peter Xu
2021-06-10 6:44 ` [PATCH 06/11] mm: page_vma_mapped_walk(): crossing page table boundary Hugh Dickins
2021-06-10 9:32 ` Kirill A. Shutemov
2021-06-10 23:02 ` Hugh Dickins
2021-06-11 11:23 ` Kirill A. Shutemov
2021-06-10 6:46 ` [PATCH 07/11] mm: page_vma_mapped_walk(): add a level of indentation Hugh Dickins
2021-06-10 9:34 ` Kirill A. Shutemov
2021-06-10 6:48 ` [PATCH 08/11] mm: page_vma_mapped_walk(): use goto instead of while (1) Hugh Dickins
2021-06-10 9:39 ` Kirill A. Shutemov
2021-06-10 6:50 ` [PATCH 09/11] mm: page_vma_mapped_walk(): get vma_address_end() earlier Hugh Dickins
2021-06-10 9:40 ` Kirill A. Shutemov
2021-06-10 6:52 ` Hugh Dickins [this message]
2021-06-10 9:42 ` [PATCH 10/11] mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes Kirill A. Shutemov
2021-06-10 6:54 ` [PATCH 11/11] mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk() Hugh Dickins
2021-06-10 9:43 ` Kirill A. Shutemov
2021-06-11 18:29 ` Hugh Dickins
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