linux-kernel - Re: Control Dependencies vs C Compilers

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Message-ID: <20201006163141.GK29330@paulmck-ThinkPad-P72>
Date:   Tue, 6 Oct 2020 09:31:41 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Willy Tarreau' <w@....eu>, 'Nick Clifton' <nickc@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "linux-toolchains@...r.kernel.org" <linux-toolchains@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "j.alglave@....ac.uk" <j.alglave@....ac.uk>,
        "luc.maranget@...ia.fr" <luc.maranget@...ia.fr>,
        "akiyks@...il.com" <akiyks@...il.com>,
        "dlustig@...dia.com" <dlustig@...dia.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: Re: Control Dependencies vs C Compilers

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