Messages in this thread | | | Date | Wed, 7 Dec 2022 12:07:46 -0500 | Subject | Re: [PATCH 1/2] sched/membarrier: Introduce MEMBARRIER_CMD_GET_REGISTRATIONS | From | Mathieu Desnoyers <> |
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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), > > /* 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 ?
> + 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 ?
> + 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 ?
> + } > + } > + 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
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