----- On Aug 10, 2016, at 3:50 AM, Peter Zijlstra peterz@infradead.org wrote:
On Tue, Aug 09, 2016 at 10:41:47PM +0000, Mathieu Desnoyers wrote:
quoted
#ifdef __LP64__
static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
{
union rseq_cpu_event u;
u.e.cpu_id = raw_smp_processor_id();
u.e.event_counter = ++t->rseq_event_counter;
if (__put_user(u.v, &t->rseq->u.v))
return false;
trace_rseq_inc(t->rseq_event_counter);
return true;
}
#else /* #ifdef __LP64__ */
static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
{
if (__put_user(raw_smp_processor_id(), &t->rseq->u.e.cpu_id))
return false;
if (__put_user(++t->rseq_event_counter, &t->rseq->u.e.event_counter))
return false;
trace_rseq_inc(t->rseq_event_counter);
return true;
}
#endif /* #else #ifdef __LP64__ */
I don't think you need to guard it (and CONFIG_64BIT is the 'right'
kernel symbol for that), 32bit should have u64 __put_user() only
implemented as 2 u32 stores.
OK, I can then simplify the implementation to:
[...]
* On 64-bit architectures, both cpu_id and event_counter can be updated
* with a single 64-bit store. On 32-bit architectures, __put_user() is
* expected to perform two 32-bit single-copy stores to guarantee
* single-copy atomicity semantics for other threads.
*/
static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
{
union rseq_cpu_event u;
u.e.cpu_id = raw_smp_processor_id();
u.e.event_counter = ++t->rseq_event_counter;
if (__put_user(u.v, &t->rseq->u.v))
return false;
trace_rseq_inc(t->rseq_event_counter);
return true;
}
Thanks!
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com