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Date: Fri, 31 Aug 2018 15:24:12 -0700 From: Tejun Heo <tj@...nel.org> To: Dennis Zhou <dennisszhou@...il.com> Cc: Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>, Josef Bacik <josef@...icpanda.com>, kernel-team@...com, linux-block@...r.kernel.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 0/3] fix blkcg offlining and destruction On Fri, Aug 31, 2018 at 04:22:41PM -0400, Dennis Zhou wrote: > 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. For patches 1-3, Acked-by: Tejun Heo <tj@...nel.org> Thanks. -- tejun
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