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    SubjectRe: [PATCH -V4 -mm] mm, swap: Fix race between swapoff and some swap operations
    On Sat, Dec 23, 2017 at 10:36:53AM +0900, Minchan Kim wrote:
    > > code path. It appears that similar situation is possible for them too.
    > >
    > > The file cache pages will be delete from file cache address_space before
    > > address_space (embedded in inode) is freed. But they will be deleted
    > > from LRU list only when its refcount dropped to zero, please take a look
    > > at put_page() and release_pages(). While address_space will be freed
    > > after putting reference to all file cache pages. If someone holds a
    > > reference to a file cache page for quite long time, it is possible for a
    > > file cache page to be in LRU list after the inode/address_space is
    > > freed.
    > >
    > > And I found inode/address_space is freed witch call_rcu(). I don't know
    > > whether this is related to page_mapping().
    > >
    > > This is just my understanding.
    >
    > Hmm, it smells like a bug of __isolate_lru_page.
    >
    > Ccing Mel:
    >
    > What locks protects address_space destroying when race happens between
    > inode trauncation and __isolate_lru_page?
    >

    I'm just back online and have a lot of catching up to do so this is a rushed
    answer and I didn't read the background of this. However the question is
    somewhat ambiguous and the scope is broad as I'm not sure which race you
    refer to. For file cache pages, I wouldnt' expect the address_space to be
    destroyed specifically as long as the inode exists which is the structure
    containing the address_space in this case. A page on the LRU being isolated
    in __isolate_lru_page will have an elevated reference count which will
    pin the inode until remove_mapping is called which holds the page lock
    while inode truncation looking at a page for truncation also only checks
    page_mapping under the page lock. Very broadly speaking, pages avoid being
    added back to an inode being freed by checking the I_FREEING state.

    Hopefully that helps while I go back to the TODO mountain.

    --
    Mel Gorman
    SUSE Labs

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