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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
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