On 2022-12-20 12:51, Michał Cłapiński wrote:
On Wed, Dec 7, 2022 at 7:04 PM Michał Cłapiński mclapinski@google.com wrote:
On Wed, Dec 7, 2022 at 6:07 PM Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
On 2022-12-07 11:43, Michal Clapinski wrote:
Provide a method to query previously issued registrations.
Signed-off-by: Michal Clapinski mclapinski@google.com
include/uapi/linux/membarrier.h | 4 ++++ kernel/sched/membarrier.c | 39 ++++++++++++++++++++++++++++++++- 2 files changed, 42 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h index 737605897f36..5f3ad6d5be6f 100644 --- a/include/uapi/linux/membarrier.h +++ b/include/uapi/linux/membarrier.h @@ -137,6 +137,9 @@ * @MEMBARRIER_CMD_SHARED: * Alias to MEMBARRIER_CMD_GLOBAL. Provided for * header backward compatibility.
- @MEMBARRIER_CMD_GET_REGISTRATIONS:
Returns a bitmask of previously issued
registration commands.
- Command to be passed to the membarrier system call. The commands need to
- be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to
@@ -153,6 +156,7 @@ enum membarrier_cmd { MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE = (1 << 6), MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ = (1 << 7), MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ = (1 << 8),
MEMBARRIER_CMD_GET_REGISTRATIONS = (1 << 9),Btw. I could do this as a flag to MEMBARRIER_CMD_QUERY instead of a separate command. Would that be preferable?
I do not think that would be better, no. We can keep it with GET_REGISTRATIONS.
/* Alias for header backward compatibility. */ MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL,diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 0c5be7ebb1dc..2ad881d07752 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -159,7 +159,8 @@ | MEMBARRIER_CMD_PRIVATE_EXPEDITED \ | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \ | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK \| MEMBARRIER_CMD_GET_REGISTRATIONS)static void ipi_mb(void *info) {
@@ -540,6 +541,40 @@ static int membarrier_register_private_expedited(int flags) return 0; }
+static int membarrier_get_registrations(void) +{
struct task_struct *p = current;struct mm_struct *mm = p->mm;int registrations_mask = 0, membarrier_state, i;static const int states[] = {MEMBARRIER_STATE_GLOBAL_EXPEDITED |MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,What is the purpose of checking for the _READY state flag as well here ?
Answered below.
MEMBARRIER_STATE_PRIVATE_EXPEDITED |MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE |MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY,MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ |MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY};static const int registration_cmds[] = {MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED,MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED,MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE,MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ};BUILD_BUG_ON(ARRAY_SIZE(states) != ARRAY_SIZE(registration_cmds));membarrier_state = atomic_read(&mm->membarrier_state);for (i = 0; i < ARRAY_SIZE(states); ++i) {if (membarrier_state & states[i]) {The mask will match if either of the flags to match are set. Is that your intent ?
Kind of, it was just the easiest to write. As explained in the cover letter, I don't really care much about the result of this while the process is running. And when the process is frozen, either state and state_ready are set or none of them.
OK
registrations_mask |= registration_cmds[i];membarrier_state &= ~states[i];So I understand that those _READY flags are there purely for making sure we clear the membarrier_state for validation that they have all been checked with the following WARN_ON_ONCE(). Am I on the right track ?
Yes, exactly. It wastes time but I'm worried about people adding new states and not updating this function. A suggestion on how to do this better (especially at compile time) would be greatly appreciated.
Although it's not a fast-path, so let's keep it this way for now.
}}WARN_ON_ONCE(membarrier_state != 0);Thanks,
Mathieu
return registrations_mask;+}
- /**
- sys_membarrier - issue memory barriers on a set of threads
- @cmd: Takes command values defined in enum membarrier_cmd.
@@ -623,6 +658,8 @@ SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id) return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, cpu_id); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ);
case MEMBARRIER_CMD_GET_REGISTRATIONS:return membarrier_get_registrations(); default: return -EINVAL; }-- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
Hi Mathieu, is there anything more you need from my side?
No, I think those patches are ok.
Thanks,
Mathieu