From: Hugh Dickins <hughd@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
Yang Shi <shy828301@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Xu <peterx@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Ira Weiny <ira.weiny@intel.com>,
Steven Price <steven.price@arm.com>,
SeongJae Park <sj@kernel.org>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Axel Rasmussen <axelrasmussen@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Minchan Kim <minchan@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Song Liu <song@kernel.org>,
Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
Russell King <linux@armlinux.org.uk>,
"David S. Miller" <davem@davemloft.net>,
Michael Ellerman <mpe@ellerman.id.au>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Jann Horn <jannh@google.com>,
linux-arm-kernel@lists.infradead.org,
sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH 05/12] powerpc: add pte_free_defer() for pgtables sharing page
Date: Mon, 29 May 2023 07:36:40 -0700 (PDT) [thread overview]
Message-ID: <a8df11d-55ae-64bc-edcb-d383a7a941ea@google.com> (raw)
In-Reply-To: <ZHSwWgLWaEd+zi/g@casper.infradead.org>
On Mon, 29 May 2023, Matthew Wilcox wrote:
> On Sun, May 28, 2023 at 11:20:21PM -0700, Hugh Dickins wrote:
> > +void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
> > +{
> > + struct page *page;
> > +
> > + page = virt_to_page(pgtable);
> > + call_rcu(&page->rcu_head, pte_free_now);
> > +}
>
> This can't be safe (on ppc). IIRC you might have up to 16x4k page
> tables sharing one 64kB page. So if you have two page tables from the
> same page being defer-freed simultaneously, you'll reuse the rcu_head
> and I cannot imagine things go well from that point.
Oh yes, of course, thanks for catching that so quickly.
So my s390 and sparc implementations will be equally broken.
>
> I have no idea how to solve this problem.
I do: I'll have to go back to the more complicated implementation we
actually ran with on powerpc - I was thinking those complications just
related to deposit/withdraw matters, forgetting the one-rcu_head issue.
It uses large (0x10000) increments of the page refcount, avoiding
call_rcu() when already active.
It's not a complication I had wanted to explain or test for now,
but we shall have to. Should apply equally well to sparc, but s390
more of a problem, since s390 already has its own refcount cleverness.
Thanks, I must dash, out much of the day.
Hugh
next prev parent reply other threads:[~2023-05-29 14:36 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-29 6:11 [PATCH 00/12] mm: free retracted page table by RCU Hugh Dickins
2023-05-29 6:14 ` [PATCH 01/12] mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s Hugh Dickins
2023-05-31 17:06 ` Jann Horn
2023-05-29 6:16 ` [PATCH 02/12] mm/pgtable: add PAE safety to __pte_offset_map() Hugh Dickins
2023-05-29 13:56 ` Matthew Wilcox
2023-05-29 6:17 ` [PATCH 03/12] arm: adjust_pte() use pte_offset_map_nolock() Hugh Dickins
2023-05-29 6:18 ` [PATCH 04/12] powerpc: assert_pte_locked() " Hugh Dickins
2023-05-29 6:20 ` [PATCH 05/12] powerpc: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-05-29 14:02 ` Matthew Wilcox
2023-05-29 14:36 ` Hugh Dickins [this message]
[not found] ` <ZHn6n5eVTsr4Wl8x@ziepe.ca>
[not found] ` <4df4909f-f5dd-6f94-9792-8f2949f542b3@google.com>
[not found] ` <ZH95oobIqN0WO5MK@ziepe.ca>
[not found] ` <ZH+DAxLhIYpTlIFc@x1n>
[not found] ` <ZH+EMp9RuEVOjVNb@ziepe.ca>
2023-06-07 3:49 ` Hugh Dickins
2023-05-29 6:21 ` [PATCH 06/12] sparc: " Hugh Dickins
2023-05-29 6:22 ` [PATCH 07/12] s390: add pte_free_defer(), with use of mmdrop_async() Hugh Dickins
[not found] ` <175ebec8-761-c3f-2d98-6c3bd87161c8@google.com>
2023-06-06 19:40 ` Gerald Schaefer
2023-06-08 3:35 ` Hugh Dickins
2023-06-08 13:58 ` Jason Gunthorpe
2023-06-08 15:47 ` Gerald Schaefer
[not found] ` <ZH99cLKeALvUCIH8@ziepe.ca>
2023-06-08 2:46 ` Hugh Dickins
2023-05-29 6:23 ` [PATCH 08/12] mm/pgtable: add pte_free_defer() for pgtable as page Hugh Dickins
2023-05-29 6:25 ` [PATCH 09/12] mm/khugepaged: retract_page_tables() without mmap or vma lock Hugh Dickins
2023-05-29 23:26 ` Peter Xu
2023-05-31 0:38 ` Hugh Dickins
2023-05-31 15:34 ` Jann Horn
2023-05-29 6:26 ` [PATCH 10/12] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() Hugh Dickins
2023-05-31 17:25 ` Jann Horn
2023-05-29 6:28 ` [PATCH 11/12] mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps() Hugh Dickins
2023-05-29 6:30 ` [PATCH 12/12] mm: delete mmap_write_trylock() and vma_try_start_write() Hugh Dickins
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