On 2018/10/4 下午10:07, Eddie Chapman wrote: > 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@xxxxxxxxx> >>>> >>>> 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@xxxxxxxxxxxxxxx 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 Hi Eddie, Yes I missed the patch dependency, thanks for the hint:-) Guoju Fang or I will take care of the back port to stable tree. Coly Li
