On 3/6/20 5:27 AM, Carlo Nonato wrote: > 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. Applied, thanks. -- Jens Axboe
