On Mon, Jan 17, 2005 at 06:50:57PM +1100, Paul Mackerras wrote:
> AFAICS on i386 the lock word, although it goes to 0 when write-locked,
> can then go negative temporarily when another cpu tries to get a read
> or write lock. So I think this should be
>
> ((signed int)(x)->lock <= 0)
I think you're right, objdump -d shows[1] _write_lock looks
something like:
lock subl $0x1000000,(%ebx)
sete %al
test %al,%al
jne out;
lock addl $0x1000000,(%ebx)
out:
so I guess it 2+ CPUs grab a write-lock at once it would indeed be
less than zero (the initial value is RW_LOCK_BIAS which is 0x1000000
in this case).
> (or the equivalent using atomic_read).
on x86 aligned-reads will be always be atomic AFAIK?
[1] Yes, I'm stupid, trying to grok the twisty-turny-maze of headers
and what not made my head hurt and objdump -d seemed easier.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
