Re: Crashes with 874bbfe600a6 in 3.18.25

[Mike Galbraith]

On Thu, 2016-02-04 at 17:39 +0100, Daniel Bilik wrote:
> On Thu, 4 Feb 2016 12:20:44 +0100
> Jan Kara <jack@xxxxxxx> wrote:
> 
> > Thanks for backport Thomas and to Mike for persistence :). I've asked my
> > friend seeing crashes with 3.18.25 to try whether this patch fixes the
> > issues. It may take some time so stay tuned...
> 
> Patch tested and it really fixes the crash we were experiencing on 3.18.25
> with commit 874bbfe+. But it seem to introduce (rather scary) regression.
> Tested host shows abnormal cpu usage in both kernel and userland under the
> same load and traffic pattern. One picture is worth a thousand words, so
> I've taken snapshots of our graphs, see here:
> http://neosystem.cz/test/linux-3.18.25/
> The host was running 3.18.25 with commit 874bbfe+ (1e7af29+ on
> 3.18-stable) reverted. With this commit included, it crashed within
> minutes. Around 13:30 we booted 3.18.25 with commit 874bbfe+ included and
> with the patch from Thomas. And around 15:40 we've booted the host with
> previous kernel, just to ensure this abnormal behaviour was really caused
> by the test kernel.
> Also interesting, in addition to high cpu usage, there is abnormally high
> number of zombie processes reported by the system.

IMHO you should restore the CC list and re-post.  (If I were the
maintainer of either the workqueue code or 3.18-stable, I'd be highly
interested in this finding).

	-Mike