Re: [PATCH 1/1] kasan: fix livelock in qlist_move_cache

[Zhouyi Zhou <zhouzhouyi@gmail.com>]

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hi,
     I will prepare the environment to let the phenonmenon reappear today
right after I reached my company.
Cheers

On Wednesday, November 29, 2017, Dmitry Vyukov <dvyukov@google.com> wrote:

> On Tue, Nov 28, 2017 at 6:56 PM, Dmitry Vyukov <dvyukov@google.com
> <javascript:;>> wrote:
> > On Tue, Nov 28, 2017 at 12:30 PM, Zhouyi Zhou <zhouzhouyi@gmail.com
> <javascript:;>> wrote:
> >> Hi,
> >>    By using perf top, qlist_move_cache occupies 100% cpu did really
> >> happen in my environment yesterday, or I
> >> won't notice the kasan code.
> >>    Currently I have difficulty to let it reappear because the frontend
> >> guy modified some user mode code.
> >>    I can repeat again and again now is
> >> kgdb_breakpoint () at kernel/debug/debug_core.c:1073
> >> 1073 wmb(); /* Sync point after breakpoint */
> >> (gdb) p quarantine_batch_size
> >> $1 = 3601946
> >>    And by instrument code, maximum
> >> global_quarantine[quarantine_tail].bytes reached is 6618208.
> >
> > On second thought, size does not matter too much because there can be
> > large objects. Quarantine always quantize by objects, we can't part of
> > an object into one batch, and another part of the object into another
> > object. But it's not a problem, because overhead per objects is O(1).
> > We can push a single 4MB object and overflow target size by 4MB and
> > that will be fine.
> > Either way, 6MB is not terribly much too. Should take milliseconds to
> process.
> >
> >
> >
> >
> >>    I do think drain quarantine right in quarantine_put is a better
> >> place to drain because cache_free is fine in
> >> that context. I am willing do it if you think it is convenient :-)
>
>
> Andrey, do you know of any problems with draining quarantine in push?
> Do you have any objections?
>
> But it's still not completely clear to me what problem we are solving.
>

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