Messages in this thread | | | Subject | Re: [PATCH] bcache: add separate workqueue for journal_write to avoid deadlock | From | Eddie Chapman <> | Date | Thu, 4 Oct 2018 15:07:54 +0100 |
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On 28/09/18 03:32, Coly Li wrote: > > On 9/27/18 11:53 PM, Eddie Chapman wrote: >> On 27/09/18 16:23, Coly Li wrote: >>> >>> On 9/27/18 9:45 PM, guoju wrote: >>>> After write SSD completed, bcache schedule journal_write work to >>>> system_wq, that is a public workqueue in system, without WQ_MEM_RECLAIM>>>> flag. system_wq is also a bound wq, and there may be no idle kworker on >>>> current processor. Creating a new kworker may unfortunately need to >>>> reclaim memory first, by shrinking cache and slab used by vfs, which >>>> depends on bcache device. That's a deadlock. >>>> >>>> This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM >>>> flag. It's rescuer thread will work to avoid the deadlock. >>>> >>>> Signed-off-by: guoju <fangguoju@gmail.com> >>> >>> Nice catch, this fix is quite important. I will try to submit to Jens >>> ASAP. >>> >>> Thanks. >>> >>> Coly Li >> >> Once this goes into 4.19, would this be a candidate for backporting to >> any stable kernels, or does it only fix something introduced in this >> cycle? >> > This bug exists in upstream for quite long time, it should be applied to > all stable kernels which it can be applied. And it is Cced to > stable@vger.kernel.org already. > > Coly Li
Thanks Coly! :-)
Just to let you know, I applied this (and couple of other cherry picks) to a couple of 4.14 boxes last night, so far so good, running without issues. However, this one needed this recent commit upstream as a pre-requisite:
16c1fdf4cfd6c0091e59b93ec2cb7e99973f8244 bcache: do not assign in if condition in bcache_init()
in order to be able to apply it.
This is because the context of the second hunk for drivers/md/bcache/super.c (in this journal_write workqueue patch) contains code added by that commit 16c1fdf4cfd6c0091e59b93ec2cb7e99973f8244.
So I guess either 16c1fdf4cfd6c0091e59b93ec2cb7e99973f8244 also needs tagging for stable, or perhaps a backport of this journal_write workqueue will have to be created for earlier kernels, with different context for that hunk?
Eddie
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