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Re: [patch V2 3/7] futex: Add op for hash preallocation

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On Sat, 7 May 2016, Thomas Gleixner wrote:
> On Fri, 6 May 2016, Darren Hart wrote:
> > > Note, that this call must be issued before the first futex operation in the
> > > process because that would automatically allocate the default sized hash.
> > 
> > So this seems like it could be tricky for the user as system libraries, like
> > glibc, make use of futexes. Can we guarantee that "sys_futex" is not called by
> > the time main() is called?
> 
> To the extent of my testing I never observed that the hash was automatically
> created when I called futex(PREALLOC) right away in main. But yes, that might
> need some thought.

Thinking more about it. If a process is single threaded and it definitely is
up to the point where it reaches main(), there is nothing which might cause a
sys_futex() call except something which would use shared futexes in the depth
of init code. I doubt that this happens, and if it does, then it's some non
standard feature^Whackery which I do not care about at all.

Thanks,

	tglx

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[patch V2 3/7] futex: Add op for hash preallocation Thomas Gleixner <tglx@linutronix.de> - 2016-05-05 22:50 +0200
  Re: [patch V2 3/7] futex: Add op for hash preallocation Darren Hart <dvhart@infradead.org> - 2016-05-06 20:20 +0200
    Re: [patch V2 3/7] futex: Add op for hash preallocation Thomas Gleixner <tglx@linutronix.de> - 2016-05-07 10:50 +0200
      Re: [patch V2 3/7] futex: Add op for hash preallocation Thomas Gleixner <tglx@linutronix.de> - 2016-05-07 13:50 +0200

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