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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Suleiman Souhlal <suleiman@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: madvise(MADV_REMOVE) deadlocks on shmem THP
Date: Thu, 14 Jan 2021 12:33:10 +0900	[thread overview]
Message-ID: <X/+7dkbhNtAVV+wd@google.com> (raw)

Hi,

We are running into lockups during the memory pressure tests on our
boards, which essentially NMI panic them. In short the test case is

- THP shmem
    echo advise > /sys/kernel/mm/transparent_hugepage/shmem_enabled

- And a user-space process doing madvise(MADV_HUGEPAGE) on new mappings,
  and madvise(MADV_REMOVE) when it wants to remove the page range

The problem boils down to the reverse locking chain:
	kswapd does

		lock_page(page) -> down_read(page->mapping->i_mmap_rwsem)

	madvise() process does

		down_write(page->mapping->i_mmap_rwsem) -> lock_page(page)



CPU0                                                       CPU1

kswapd                                                     vfs_fallocate()
 shrink_node()                                              shmem_fallocate()
  shrink_active_list()                                       unmap_mapping_range()
   page_referenced() << lock page:PG_locked >>                unmap_mapping_pages()  << down_write(mapping->i_mmap_rwsem) >>
    rmap_walk_file()                                           zap_page_range_single()
     down_read(mapping->i_mmap_rwsem) << W-locked on CPU1>>     unmap_page_range()
      rwsem_down_read_failed()                                   __split_huge_pmd()
       __rwsem_down_read_failed_common()                          __lock_page()  << PG_locked on CPU0 >>
        schedule()                                                 wait_on_page_bit_common()
                                                                    io_schedule()

	-ss


             reply	other threads:[~2021-01-14  3:33 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14  3:33 Sergey Senozhatsky [this message]
2021-01-14  4:31 ` Hugh Dickins
2021-01-14  5:38   ` Sergey Senozhatsky

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