Re: [PATCH v4 3/4] futex: Document ordering guarantees

From: Darren Hart
Date: Thu Dec 19 2013 - 16:08:01 EST


On Thu, 2013-12-19 at 13:00 -0800, Davidlohr Bueso wrote:
> On Thu, 2013-12-19 at 12:51 -0800, Randy Dunlap wrote:
> > On 12/19/13 12:45, Davidlohr Bueso wrote:
> > > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > >
> > > That's essential, if you want to hack on futexes.
> > >
> > > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > > Cc: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
> > > Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > > Cc: Mike Galbraith <efault@xxxxxx>
> > > Cc: Jeff Mahoney <jeffm@xxxxxxxx>
> > > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Scott Norton <scott.norton@xxxxxx>
> > > Cc: Tom Vaden <tom.vaden@xxxxxx>
> > > Cc: Aswin Chandramouleeswaran <aswin@xxxxxx>
> > > Cc: Waiman Long <Waiman.Long@xxxxxx>
> > > Cc: Jason Low <jason.low2@xxxxxx>
> > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
> > > ---
> > > kernel/futex.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 57 insertions(+)
> > >
> > > diff --git a/kernel/futex.c b/kernel/futex.c
> > > index 577481d..af1fc31 100644
> > > --- a/kernel/futex.c
> > > +++ b/kernel/futex.c
> > > @@ -69,6 +69,63 @@
> > >
> > > #include "locking/rtmutex_common.h"
> > >
> > > +/*
> > > + * Basic futex operation and ordering guarantees:
> > > + *
> > > + * The waiter reads the futex value in user space and calls
> > > + * futex_wait(). It computes the hash bucket and acquires the hash
> >
> > does It
> > refer to "the waiter" or to futex_wait()?
> > I read it as referring to the waiter, but ISTM that the comments are using It
> > to refer to futex_wait()... ???
> >
>
> Yes, it refers to futex_wait(), which IMO in a futex context is pretty
> clear.


Agreed.


--
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel


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