Messages in this thread | | | Date | Wed, 10 Aug 2016 13:26:04 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH v7 1/7] Restartable sequences system call |
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----- 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: >> #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
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