On Mon, Jan 06, 2025 at 05:12:57PM -0700, Jeff Law wrote:
>
>
> On 1/6/25 6:03 AM, Maciej W. Rozycki wrote:
> > With non-BWX Alpha implementations we have a problem of data races where
> > a 8-bit byte or 16-bit word quantity is to be written to memory in that
> > in those cases we use an unprotected RMW access of a 32-bit longword or
> > 64-bit quadword width. If contents of the longword or quadword accessed
> > outside the byte or word to be written are changed midway through by a
> > concurrent write executing on the same CPU such as by a signal handler
> > or a parallel write executing on another CPU such as by another thread
> > or via a shared memory segment, then the concluding write of the RMW
> > access will clobber them. This is especially important for the safety
> > of RCU algorithms, but is otherwise an issue anyway.
> But in the case of concurrent accesses, shouldn't these objects be declared
> as atomic? Similarly for objects potentially accessed in a signal hnadler
> shouldn't they be accessed via sig_atomic_t?
>
> Point being I'm not 100% sure we really need to tackle this problem in a
> fully generic manner for all 8/16 bit accesses
>
> What am I missing here?
Doesn't the behavior Maciej is describing constitute a data race injected
by the compiler? As of C11 and C++11, this is forbidden, correct?
Thanx, Paul
