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

From: Thomas Gleixner
Date: Sat May 07 2016 - 07:44:07 EST

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.