Re: [PATCH] mm,page_alloc: softlockup on warn_alloc on

[Michal Hocko <mhocko@suse.com>]

On Fri 15-09-17 21:09:29, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Fri 15-09-17 20:38:49, Tetsuo Handa wrote:
> > [...]
> > > You said "identify _why_ we see the lockup trigerring in the first
> > > place" without providing means to identify it. Unless you provide
> > > means to identify it (in a form which can be immediately and easily
> > > backported to 4.9 kernels; that is, backporting not-yet-accepted
> > > printk() offloading patchset is not a choice), this patch cannot be
> > > refused.
> > 
> > I fail to see why. It simply workarounds an existing problem elsewhere
> > in the kernel without deeper understanding on where the problem is. You
> > can add your own instrumentation to debug and describe the problem. This
> > is no different to any other kernel bugs...
> 
> Please do show us your patch for that. Normal users cannot afford developing
> such instrumentation to debug and describe the problem.

Stop this nonsense already! Any kernel bug/lockup needs a debugging
which might be non-trivial and it is necessary to understand the real
culprit. We do not add random hacks to silence a problem. We aim at
fixing it!
 
> > If our printk implementation is so weak it cannot cope with writers then
> > that should be fixed without spreading hacks in different subsystems. If
> > the lockup is a real problem under normal workloads (rather than
> > artificial ones) then we should try to throttle more aggresively.
> 
> No throttle please. Throttling makes warn_alloc() more and more useless.

so does try_lock approach...

-- 
Michal Hocko
SUSE Labs

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