Nick Piggin wrote: > Satyam Sharma wrote: >> And we have driver / subsystem maintainers such as Stefan >> coming up and admitting that often a lot of code that's written to use >> atomic_read() does assume the read will not be elided by the compiler. > > So these are broken on i386 and x86-64?
The ieee1394 and firewire subsystems have open, undiagnosed bugs, also on i386 and x86-64. But whether there is any bug because of wrong assumptions about atomic_read among them, I don't know. I don't know which assumptions the authors made, I only know that I wasn't aware of all the properties of atomic_read until now. > Are they definitely safe on SMP and weakly ordered machines with > just a simple compiler barrier there? Because I would not be > surprised if there are a lot of developers who don't really know > what to assume when it comes to memory ordering issues. > > This is not a dig at driver writers: we still have memory ordering > problems in the VM too (and probably most of the subtle bugs in > lockless VM code are memory ordering ones). Let's not make up a > false sense of security and hope that sprinkling volatile around > will allow people to write bug-free lockless code. If a writer > can't be bothered reading API documentation ...or, if there is none, the implementation specification (as in case of the atomic ops), or, if there is none, the implementation (as in case of a some infrastructure code here and there)... > and learning the Linux memory model, they can still be productive > writing safely locked code. Provided they are aware that they might not have the full picture of the lockless primitives. :-) -- Stefan Richter -=====-=-=== =--- =---= http://arcgraph.de/sr/ - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
