On Sat, Apr 25, 2015 at 08:50:49AM -0400, Rik van Riel wrote: > On 04/25/2015 05:43 AM, Heiko Carstens wrote: > > ...the READ_ONCE() doesn't give you any guarantees about reading > > tsk->acct_timexpd in an atomic way. > > Well, actually you don't need atomic semantics, but only to make sure that > > the read access happens with a single instruction, since you want to protect > > against interrupts. > > But still: if the size of acct_timexpd is 64 bit READ_ONCE() may still > > result > > in two instructions on 32 bit architectures. > > (or isn't there currently no 32 bit architecture with 64 bit cputime_t > > left?) > > Even if there is (maybe some ARM system?), can we even guarantee > that a single instruction to read 64 bits exists on such a system?
I wouldn't bet on it. I can only talk for s390 and there is an instruction available which would do that. But since s390 is now a 64 bit only architecture it doesn't matter anyway. For other architectures I'd say: no, you can't rely on that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
