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Date:   Tue, 6 Oct 2020 09:31:41 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Willy Tarreau' <w@1wt.eu>, 'Nick Clifton' <nickc@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "stern@rowland.harvard.edu" <stern@rowland.harvard.edu>,
        "linux-toolchains@vger.kernel.org" <linux-toolchains@vger.kernel.org>,
        Will Deacon <will@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "parri.andrea@gmail.com" <parri.andrea@gmail.com>,
        "boqun.feng@gmail.com" <boqun.feng@gmail.com>,
        "npiggin@gmail.com" <npiggin@gmail.com>,
        "dhowells@redhat.com" <dhowells@redhat.com>,
        "j.alglave@ucl.ac.uk" <j.alglave@ucl.ac.uk>,
        "luc.maranget@inria.fr" <luc.maranget@inria.fr>,
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        "joel@joelfernandes.org" <joel@joelfernandes.org>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>
Subject: Re: Control Dependencies vs C Compilers
Message-ID: <20201006163141.GK29330@paulmck-ThinkPad-P72>
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On Tue, Oct 06, 2020 at 04:22:10PM +0000, David Laight wrote:
> From: Willy Tarreau
> > Sent: 06 October 2020 17:11
> > 
> > On Tue, Oct 06, 2020 at 08:50:52AM -0700, Paul E. McKenney wrote:
> > > Comparing 25+ assembly languages to but two compilers most definitely
> > > motivates looking hard at doing something with the compilers.
> > 
> > +1, especially since the kernel is not special; anyone working with
> > threads faces the same issues in userland, which are often hidden
> > behind the implicit whole-memory clobbers of certain operations or
> > the call to mutex manipulation functions, but which become a reality
> > again as soon as you go slightly away from these and try to use
> > lockless mechanisms.
> 
> AFAICT most windows and android apps completely ignore the problem
> of thread locking - which is why the crash and lock up all the time :-)
> 
> I've spent most of the day looking at some library traces from a
> customer bug.
> I almost suspect a bug in the pthread mutex code on their system.
> They are using a nice, modern, 3.10.0-957.el7.x86_64 kernel.

It would be good if the compiler were more helpful!  Failing that, if
-something- could be more helpful!!!

							Thanx, Paul