Re: ipc,sem: sysv semaphore scalability

[Emmanuel Benisty]

Hi Linus,

On Sun, Mar 31, 2013 at 12:22 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Mar 29, 2013 at 10:57 PM, Emmanuel Benisty <benisty.e@xxxxxxxxx> wrote:
>> On Sat, Mar 30, 2013 at 12:10 PM, Linus Torvalds
>>>
>>> This came from the gcc build?
>>
>> yes, very early in the build process, IIRC this line was repeated a
>> few times and the build just stalled.
>
> Ok, we're bringing out the crazy hacks now.
>
> The attached patch is just insane, doesn't really even work in
> general, and only even compiles on 64-bit. But it should work in
> *practice* to find if somebody adds the same RCU head to the RCU lists
> twice, and ignore the second time it happens (and give a warning that
> hopefully pinpoints the backtrace).
>
> It's ugly. It's broken. It may not work. In other words, I'm not proud
> of it. But you seem to be the only one able to trigger the issue
> easily, willing to try crazy crap, so "tag, you're it". Maybe this
> gives us more information. And maybe it doesn't, and I'm totally wrong
> about the whole "rcu head added twice" theory.

That's all I could get so far:
https://gist.github.com/anonymous/5279255

Losing wireless is generally the start signal of controlled demolition
of the machine.
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