shmem_getpage_locked() / swapin_readahead() race in 2.4.4-pre3

From: Marcelo Tosatti (marcelo@conectiva.com.br)
Date: Sat Apr 14 2001 - 11:59:40 EDT

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    Hi,

    There is a nasty race between shmem_getpage_locked() and
    swapin_readahead() with the new shmem code (introduced in 2.4.3-ac3 and
    merged in the main tree in 2.4.4-pre3):

    shmem_getpage_locked() finds a page in the swapcache and moves it to the
    pagecache as an shmem page, freeing the swapcache and the swap map entry
    for this page. (which causes a BUG() in mm/shmem.c:353 since the swap
    map entry is being used)

    In the meanwhile, swapin_readahead() is allocating a page and adding it to
    the swapcache.

    I don't see any clean fix for this one.

    Suggestions ?

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