• Mikulas Patocka's avatar
    dm crypt: fix mempool deadlock · aeb2deae
    Mikulas Patocka authored
    This patch fixes a possible deadlock in dm-crypt's mempool use.
    
    Currently, dm-crypt reserves a mempool of MIN_BIO_PAGES reserved pages.
    It allocates first MIN_BIO_PAGES with non-failing allocation (the allocation
    cannot fail and waits until the mempool is refilled). Further pages are
    allocated with different gfp flags that allow failing.
    
    Because allocations may be done in parallel, this code can deadlock. Example:
    There are two processes, each tries to allocate MIN_BIO_PAGES and the processes
    run simultaneously.
    It may end up in a situation where each process allocates (MIN_BIO_PAGES / 2)
    pages. The mempool is exhausted. Each process waits for more pages to be freed
    to the mempool, which never happens.
    
    To avoid this deadlock scenario, this patch changes the code so that only
    the first page is allocated with non-failing gfp mask. Allocation of further
    pages may fail.
    Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Cc: stable@kernel.org
    Signed-off-by: default avatarMilan Broz <mbroz@redhat.com>
    Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
    aeb2deae
dm-crypt.c 44 KB