Re: [PATCH] make atomic_t volatile on all architectures

[Linus Torvalds]

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. 

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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/