Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1741813

Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message

Show all headers | View raw

Yang Shi wrote:
> On 9/28/17 12:57 PM, Tetsuo Handa wrote:
> > Yang Shi wrote:
> >> On 9/27/17 9:36 PM, Tetsuo Handa wrote:
> >>> On 2017/09/28 6:46, Yang Shi wrote:
> >>>> Changelog v7 -> v8:
> >>>> * Adopted Michal’s suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path.
> >>>
> >>> Holding slab_mutex inside dump_unreclaimable_slab() was refrained since V2
> >>> because there are
> >>>
> >>> 	mutex_lock(&slab_mutex);
> >>> 	kmalloc(GFP_KERNEL);
> >>> 	mutex_unlock(&slab_mutex);
> >>>
> >>> users. If we call dump_unreclaimable_slab() for non OOM panic path, aren't we
> >>> introducing a risk of crash (i.e. kernel panic) for regular OOM path?
> >>
> >> I don't see the difference between regular oom path and oom path other
> >> than calling panic() at last.
> >>
> >> And, the slab dump may be called by panic path too, it is for both
> >> regular and panic path.
> > 
> > Calling a function that might cause kerneloops immediately before calling panic()
> > would be tolerable, for the kernel will panic after all. But calling a function
> > that might cause kerneloops when there is no plan to call panic() is a bug.
> 
> I got your point. slab_mutex is used to protect the list of all the  
> slabs, since we are already in oom, there should be not kmem cache  
> destroy happen during the list traverse. And, list_for_each_entry() has  
> been replaced to list_for_each_entry_safe() to make the traverse more  
> robust.

I consider that OOM event and kmem chache destroy event can run concurrently
because slab_mutex is not held by OOM event (and unfortunately cannot be held
due to possibility of deadlock) in order to protect the list of all the slabs.

I don't think replacing list_for_each_entry() with list_for_each_entry_safe()
makes the traverse more robust, for list_for_each_entry_safe() does not defer
freeing of memory used by list element. Rather, replacing list_for_each_entry()
with list_for_each_entry_rcu() (and making relevant changes such as
rcu_read_lock()/rcu_read_unlock()/synchronize_rcu()) will make the traverse safe.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-09-27 23:50 +0200
  [PATCH 2/2] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory "Yang Shi" <yang.s@alibaba-inc.com> - 2017-09-27 23:50 +0200
    Re: [PATCH 2/2] mm: oom: show unreclaimable slab info when unreclaimable  slabs > user memory Christopher Lameter <cl@linux.com> - 2017-10-01 08:20 +0200
  Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-09-28 06:40 +0200
    Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-09-28 19:50 +0200
      Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-09-28 22:00 +0200
        Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-09-28 22:30 +0200
          Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-09-28 22:50 +0200
            Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-09-30 00:20 +0200
              Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-09-30 13:10 +0200
                Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-10-02 22:50 +0200
    Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message Michal Hocko <mhocko@kernel.org> - 2017-10-02 13:30 +0200
      Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom  message "Yang Shi" <yang.s@alibaba-inc.com> - 2017-10-02 22:50 +0200

csiph-web