----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@xxxxxxxxxxxxxxxxxx wrote:
> On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
>> Userspace applications should be allowed to expect the membarrier system
>> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
>> nohz_full CPUs, but synchronize_sched() does not take those into
>> account.
>>
>> Given that we do not want unrelated processes to be able to affect
>> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
>> is invoked on a kernel with enabled nohz_full CPUs.
>>
>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>> CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>
> Acked-by: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Hi Paul,
Do you plan to pick it up through your tree, or I should sent
it directly to Linus ?
Thanks,
Mathieu
>
>> CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> CC: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
>> CC: <stable@xxxxxxxxxxxxxxx> [3.10+]
>> ---
>> kernel/membarrier.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
>> index 536c727..9f9284f 100644
>> --- a/kernel/membarrier.c
>> +++ b/kernel/membarrier.c
>> @@ -16,6 +16,7 @@
>>
>> #include <linux/syscalls.h>
>> #include <linux/membarrier.h>
>> +#include <linux/tick.h>
>>
>> /*
>> * Bitmask made from a "or" of all commands within enum membarrier_cmd,
>> @@ -51,6 +52,9 @@
>> */
>> SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>> {
>> + /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
>> + if (tick_nohz_full_enabled())
>> + return -ENOSYS;
>> if (unlikely(flags))
>> return -EINVAL;
>> switch (cmd) {
>> --
>> 2.1.4
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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