• C
    block, bfq: fix overwrite of bfq_group pointer in bfq_find_set_group() · 8cf52b47
    Carlo Nonato 提交于
    task #28557799
    
    [ Upstream commit 14afc59361976c0ba39e3a9589c3eaa43ebc7e1d ]
    
    The bfq_find_set_group() function takes as input a blkcg (which represents
    a cgroup) and retrieves the corresponding bfq_group, then it updates the
    bfq internal group hierarchy (see comments inside the function for why
    this is needed) and finally it returns the bfq_group.
    In the hierarchy update cycle, the pointer holding the correct bfq_group
    that has to be returned is mistakenly used to traverse the hierarchy
    bottom to top, meaning that in each iteration it gets overwritten with the
    parent of the current group. Since the update cycle stops at root's
    children (depth = 2), the overwrite becomes a problem only if the blkcg
    describes a cgroup at a hierarchy level deeper than that (depth > 2). In
    this case the root's child that happens to be also an ancestor of the
    correct bfq_group is returned. The main consequence is that processes
    contained in a cgroup at depth greater than 2 are wrongly placed in the
    group described above by BFQ.
    
    This commits fixes this problem by using a different bfq_group pointer in
    the update cycle in order to avoid the overwrite of the variable holding
    the original group reference.
    Reported-by: NKwon Je Oh <kwonje.oh2@gmail.com>
    Signed-off-by: NCarlo Nonato <carlo.nonato95@gmail.com>
    Signed-off-by: NPaolo Valente <paolo.valente@linaro.org>
    Signed-off-by: NJens Axboe <axboe@kernel.dk>
    Signed-off-by: NSasha Levin <sashal@kernel.org>
    Signed-off-by: NJeffle Xu <jefflexu@linux.alibaba.com>
    Acked-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
    8cf52b47
bfq-cgroup.c 33.6 KB