From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerry Jiang Subject: Re: [PATCH] make atomic_t volatile on all architectures Date: Thu, 9 Aug 2007 12:59:20 +0800 Message-ID: <20070809125920.37eb6e6d.wjiang@resilience.com> References: <20070808230733.GA17270@shell.boston.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Chris Snook , akpm@linux-foundation.org, ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, schwidefsky@de.ibm.com, wensong@linux-vs.org, horms@verge.net.au, cfriesen@nortel.com, zlynx@acm.org To: Linus Torvalds Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 8 Aug 2007 21:18:25 -0700 (PDT) Linus Torvalds wrote: > > > On Wed, 8 Aug 2007, Chris Snook wrote: > > > > Some architectures currently do not declare the contents of an atomic_t to be > > volatile. This causes confusion since atomic_read() might not actually read > > anything if an optimizing compiler re-uses a value stored in a register, which > > can break code that loops until something external changes the value of an > > atomic_t. > > I'd be *much* happier with "atomic_read()" doing the "volatile" instead. > > The fact is, volatile on data structures is a bug. It's a wart in the C > language. It shouldn't be used. Why? It's a wart! Is it due to unclear C standard on volatile related point? Why the *volatile-accesses-in-code* is acceptable, does C standard make it clear? -- Jerry > > Volatile accesses in *code* can be ok, and if we have "atomic_read()" > expand to a "*(volatile int *)&(x)->value", then I'd be ok with that. > > But marking data structures volatile just makes the compiler screw up > totally, and makes code for initialization sequences etc much worse. > > Linus