• Joe Thornber's avatar
    dm btree: fix a recursion depth bug in btree walking code · dd6f0932
    Joe Thornber authored
    commit 9b460d36 upstream.
    
    The walk code was using a 'ro_spine' to hold it's locked btree nodes.
    But this data structure is designed for the rolling lock scheme, and
    as such automatically unlocks blocks that are two steps up the call
    chain.  This is not suitable for the simple recursive walk algorithm,
    which retraces its steps.
    
    This code is only used by the persistent array code, which in turn is
    only used by dm-cache.  In order to trigger it you need to have a
    mapping tree that is more than 2 levels deep; which equates to 8-16
    million cache blocks.  For instance a 4T ssd with a very small block
    size of 32k only just triggers this bug.
    
    The fix just places the locked blocks on the stack, and stops using
    the ro_spine altogether.
    Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
    dd6f0932
dm-btree-spine.c 5.13 KB