Messages in this thread | | | Date | Wed, 9 Jun 2021 13:17:59 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2 01/10] mm/thp: fix __split_huge_pmd_locked() on shmem migration entry (fwd) |
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On Tue, Jun 08, 2021 at 09:05:21PM -0700, Hugh Dickins wrote: > > > ---------- Forwarded message ---------- > Date: Tue, 8 Jun 2021 21:00:12 -0700 (PDT) > 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>, > Naoya Horiguchi <naoya.horiguchi@nec.com>, > Alistair Popple <apopple@nvidia.com>, Ralph Campbell <rcampbell@nvidia.com>, > Zi Yan <ziy@nvidia.com>, Miaohe Lin <linmiaohe@huawei.com>, > Minchan Kim <minchan@kernel.org>, Jue Wang <juew@google.com>, > Peter Xu <peterx@redhat.com>, Jan Kara <jack@suse.cz>, > Shakeel Butt <shakeelb@google.com>, Oscar Salvador <osalvador@suse.de> > Subject: [PATCH v2 01/10] mm/thp: fix __split_huge_pmd_locked() on shmem > migration entry > > Stressing huge tmpfs page migration racing hole punch often crashed on the > VM_BUG_ON(!pmd_present) in pmdp_huge_clear_flush(), with DEBUG_VM=y kernel; > or shortly afterwards, on a bad dereference in __split_huge_pmd_locked() > when DEBUG_VM=n. They forgot to allow for pmd migration entries in the > non-anonymous case. > > Full disclosure: those particular experiments were on a kernel with more > relaxed mmap_lock and i_mmap_rwsem locking, and were not repeated on the > vanilla kernel: it is conceivable that stricter locking happens to avoid > those cases, or makes them less likely; but __split_huge_pmd_locked() > already allowed for pmd migration entries when handling anonymous THPs, > so this commit brings the shmem and file THP handling into line. > > And while there: use old_pmd rather than _pmd, as in the following blocks; > and make it clearer to the eye that the !vma_is_anonymous() block is > self-contained, making an early return after accounting for unmapping. > > Fixes: e71769ae5260 ("mm: enable thp migration for shmem thp") > Signed-off-by: Hugh Dickins <hughd@google.com> > Cc: <stable@vger.kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-- Kirill A. Shutemov
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