Hi everyone, This is a split of an earlier series I sent out [1] containing the first 3 patches with fixes from feedback. This series tackles the first problem where blkcgs were not being destroyed. There is a regression in blkcg destruction where references weren't properly put causing blkcgs to never be destroyed. Previously, blkgs were destroyed during offlining of the blkcg. This puts back the blkcg reference a blkg holds allowing blkcg ref to reach zero. Then, blkcg_css_free() is called as part of the final cleanup. To address the problem, 0001 reverts the broken commit, 0002 delays blkg destruction until writeback has finished, and 0003 closes the window on a race condition between a css migration and dying, and blkg association. This should fix the issue where blkg_get() was getting called when a blkcg had already begun exiting. If a bio finds itself here, it will just fall back to root. Oddly enough at one point, blk-throttle was using policy data from and associating with potentially different blkgs, thus how this was exposed. [1] https://lore.kernel.org/lkml/20180831015356.69796-1-dennisszhou@xxxxxxxxx/T This patchset contains the following 3 patches: 0001-Revert-blk-throttle-fix-race-between-blkcg_bio_issue.patch 0002-blkcg-delay-blkg-destruction-until-after-writeback-h.patch 0003-blkcg-use-tryget-logic-when-associating-a-blkg-with-.patch 0001 reverts the broken commit. 0002 delays blkg destruction until after writeback. 0003 fixes a race condition for ongoing IO and blkcg destruction. This patchset is on top of axboe#for-4.19/block b86d865cb1ca. diffstats below: Dennis Zhou (Facebook) (3): Revert "blk-throttle: fix race between blkcg_bio_issue_check() and cgroup_rmdir()" blkcg: delay blkg destruction until after writeback has finished blkcg: use tryget logic when associating a blkg with a bio block/bio.c | 3 +- block/blk-cgroup.c | 105 +++++++++++++++++-------------------- block/blk-throttle.c | 5 +- include/linux/blk-cgroup.h | 45 +++++++++++++++- mm/backing-dev.c | 5 ++ 5 files changed, 102 insertions(+), 61 deletions(-) Thanks, Dennis
