Re: [RFC PATCH 2/2] membarrier: provide register sync core cmd

[Paul E. McKenney]

On Sun, Aug 27, 2017 at 08:52:58PM +0000, Mathieu Desnoyers wrote:
> ----- On Aug 27, 2017, at 1:35 PM, Paul E. McKenney paulmck@xxxxxxxxxxxxxxxxxx wrote:
> 
> > On Sun, Aug 27, 2017 at 12:54:04PM -0700, Mathieu Desnoyers wrote:
> >> Add a new MEMBARRIER_CMD_REGISTER_SYNC_CORE command to the membarrier
> >> system call. It allows processes to register their intent to have their
> >> threads issue core serializing barriers in addition to memory barriers
> >> whenever a membarrier command is performed.
> >> 
> >> It is relevant for reclaim of JIT code, which requires to issue core
> >> serializing barriers on all threads running on behalf of a process
> >> after ensuring the old code is not visible anymore, before re-using
> >> memory for new code.
> >> 
> >> When a processes returns from a MEMBARRIER_CMD_REGISTER_SYNC_CORE
> >> command, it is guaranteed that all following MEMBARRIER_CMD_SHARED and
> >> MEMBARRIER_CMD_PRIVATE_EXPEDITED issue core serializing barriers, in
> >> addition to the memory barriers, on all of its running threads.
> > 
> > I have queued both of these for testing and review:
> > 
> >  git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> >  f54cf5123eb9 ("membarrier: Speed up single-threaded private cmd")
> >  0d6eb99818da ("membarrier: Provide register sync core cmd")
> > 
> > Could the people who asked for this please test it?  The second commit
> > is non-obvious enough to need some careful review and intensive testing
> > before I can in good conscious pass it upstream.
> 
> Thanks Paul!
> 
> Can you pick up my v2 instead ? I added benchmarks in the changelog and
> documented the new command in the membarrier public header. No changes
> otherwise.

It looks like 0day Test Robot also wants some additional header files.
Could you please send me a v3 with its complaints addressed?

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> > 
> >							Thanx, Paul
> > 
> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> >> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >> CC: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> >> CC: Boqun Feng <boqun.feng@xxxxxxxxx>
> >> CC: Andrew Hunter <ahh@xxxxxxxxxx>
> >> CC: Maged Michael <maged.michael@xxxxxxxxx>
> >> CC: gromer@xxxxxxxxxx
> >> CC: Avi Kivity <avi@xxxxxxxxxxxx>
> >> CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> >> CC: Paul Mackerras <paulus@xxxxxxxxx>
> >> CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> >> CC: Dave Watson <davejwatson@xxxxxx>
> >> CC: Andy Lutomirski <luto@xxxxxxxxxx>
> >> CC: Will Deacon <will.deacon@xxxxxxx>
> >> CC: Hans Boehm <hboehm@xxxxxxxxxx>
> >> ---
> >>  fs/exec.c                       |  1 +
> >>  include/linux/sched.h           | 52 +++++++++++++++++++++++++++++++++++++++++
> >>  include/uapi/linux/membarrier.h |  1 +
> >>  kernel/fork.c                   |  2 ++
> >>  kernel/sched/core.c             |  3 +++
> >>  kernel/sched/membarrier.c       | 37 ++++++++++++++++++++++++++---
> >>  6 files changed, 93 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/fs/exec.c b/fs/exec.c
> >> index 62175cbcc801..a4ab3253bac7 100644
> >> --- a/fs/exec.c
> >> +++ b/fs/exec.c
> >> @@ -1794,6 +1794,7 @@ static int do_execveat_common(int fd, struct filename
> >> *filename,
> >>  	/* execve succeeded */
> >>  	current->fs->in_exec = 0;
> >>  	current->in_execve = 0;
> >> +	membarrier_execve(current);
> >>  	acct_update_integrals(current);
> >>  	task_numa_free(current);
> >>  	free_bprm(bprm);
> >> diff --git a/include/linux/sched.h b/include/linux/sched.h
> >> index 8337e2db0bb2..b1ecdc4e8b84 100644
> >> --- a/include/linux/sched.h
> >> +++ b/include/linux/sched.h
> >> @@ -1086,6 +1086,9 @@ struct task_struct {
> >>  	/* Used by LSM modules for access restriction: */
> >>  	void				*security;
> >>  #endif
> >> +#ifdef CONFIG_MEMBARRIER
> >> +	int membarrier_sync_core;
> >> +#endif
> >> 
> >>  	/*
> >>  	 * New fields for task_struct should be added above here, so that
> >> @@ -1623,4 +1626,53 @@ extern long sched_getaffinity(pid_t pid, struct cpumask
> >> *mask);
> >>  #define TASK_SIZE_OF(tsk)	TASK_SIZE
> >>  #endif
> >> 
> >> +#ifdef CONFIG_MEMBARRIER
> >> +static inline void membarrier_fork(struct task_struct *t,
> >> +		unsigned long clone_flags)
> >> +{
> >> +	/*
> >> +	 * Coherence of membarrier_sync_core against thread fork is
> >> +	 * protected by siglock. membarrier_fork is called with siglock
> >> +	 * held.
> >> +	 */
> >> +	t->membarrier_sync_core = current->membarrier_sync_core;
> >> +}
> >> +static inline void membarrier_execve(struct task_struct *t)
> >> +{
> >> +	t->membarrier_sync_core = 0;
> >> +}
> >> +static inline void membarrier_sched_out(struct task_struct *t)
> >> +{
> >> +	/*
> >> +	 * Core serialization is performed before the memory barrier
> >> +	 * preceding the store to rq->curr.
> >> +	 */
> >> +	if (unlikely(READ_ONCE(t->membarrier_sync_core)))
> >> +		sync_core();
> >> +}
> >> +static inline void membarrier_sched_in(struct task_struct *t)
> >> +{
> >> +	/*
> >> +	 * Core serialization is performed after the memory barrier
> >> +	 * following the store to rq->curr.
> >> +	 */
> >> +	if (unlikely(READ_ONCE(t->membarrier_sync_core)))
> >> +		sync_core();
> >> +}
> >> +#else
> >> +static inline void membarrier_fork(struct task_struct *t,
> >> +		unsigned long clone_flags)
> >> +{
> >> +}
> >> +static inline void membarrier_execve(struct task_struct *t)
> >> +{
> >> +}
> >> +static inline void membarrier_sched_out(struct task_struct *t)
> >> +{
> >> +}
> >> +static inline void membarrier_sched_in(struct task_struct *t)
> >> +{
> >> +}
> >> +#endif
> >> +
> >>  #endif
> >> diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h
> >> index 6d47b3249d8a..bc26fcf8fb7b 100644
> >> --- a/include/uapi/linux/membarrier.h
> >> +++ b/include/uapi/linux/membarrier.h
> >> @@ -67,6 +67,7 @@ enum membarrier_cmd {
> >>  	/* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
> >>  	/* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
> >>  	MEMBARRIER_CMD_PRIVATE_EXPEDITED	= (1 << 3),
> >> +	MEMBARRIER_CMD_REGISTER_SYNC_CORE	= (1 << 4),
> >>  };
> >> 
> >>  #endif /* _UAPI_LINUX_MEMBARRIER_H */
> >> diff --git a/kernel/fork.c b/kernel/fork.c
> >> index 17921b0390b4..713b3c932671 100644
> >> --- a/kernel/fork.c
> >> +++ b/kernel/fork.c
> >> @@ -1840,6 +1840,8 @@ static __latent_entropy struct task_struct *copy_process(
> >>  	 */
> >>  	copy_seccomp(p);
> >> 
> >> +	membarrier_fork(p, clone_flags);
> >> +
> >>  	/*
> >>  	 * Process group and session signals need to be delivered to just the
> >>  	 * parent before the fork or both the parent and the child after the
> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >> index 0e36d9960d91..3ca27d066950 100644
> >> --- a/kernel/sched/core.c
> >> +++ b/kernel/sched/core.c
> >> @@ -3292,6 +3292,8 @@ static void __sched notrace __schedule(bool preempt)
> >>  	local_irq_disable();
> >>  	rcu_note_context_switch(preempt);
> >> 
> >> +	membarrier_sched_out(prev);
> >> +
> >>  	/*
> >>  	 * Make sure that signal_pending_state()->signal_pending() below
> >>  	 * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
> >> @@ -3364,6 +3366,7 @@ static void __sched notrace __schedule(bool preempt)
> >> 
> >>  		/* Also unlocks the rq: */
> >>  		rq = context_switch(rq, prev, next, &rf);
> >> +		membarrier_sched_in(next);
> >>  	} else {
> >>  		rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
> >>  		rq_unlock_irq(rq, &rf);
> >> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> >> index 7eec6914d2d2..f128caf64b49 100644
> >> --- a/kernel/sched/membarrier.c
> >> +++ b/kernel/sched/membarrier.c
> >> @@ -25,12 +25,16 @@
> >>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
> >>   * except MEMBARRIER_CMD_QUERY.
> >>   */
> >> -#define MEMBARRIER_CMD_BITMASK	\
> >> -	(MEMBARRIER_CMD_SHARED | MEMBARRIER_CMD_PRIVATE_EXPEDITED)
> >> +#define MEMBARRIER_CMD_BITMASK			\
> >> +	(MEMBARRIER_CMD_SHARED			\
> >> +	| MEMBARRIER_CMD_PRIVATE_EXPEDITED	\
> >> +	| MEMBARRIER_CMD_REGISTER_SYNC_CORE)
> >> 
> >>  static void ipi_mb(void *info)
> >>  {
> >> -	smp_mb();	/* IPIs should be serializing but paranoid. */
> >> +	/* IPIs should be serializing but paranoid. */
> >> +	smp_mb();
> >> +	sync_core();
> >>  }
> >> 
> >>  static void membarrier_private_expedited(void)
> >> @@ -96,6 +100,30 @@ static void membarrier_private_expedited(void)
> >>  	smp_mb();	/* exit from system call is not a mb */
> >>  }
> >> 
> >> +static void membarrier_register_sync_core(void)
> >> +{
> >> +	struct task_struct *p = current, *t;
> >> +
> >> +	if (get_nr_threads(p) == 1) {
> >> +		p->membarrier_sync_core = 1;
> >> +		return;
> >> +	}
> >> +
> >> +	/*
> >> +	 * Coherence of membarrier_sync_core against thread fork is
> >> +	 * protected by siglock.
> >> +	 */
> >> +	spin_lock(&p->sighand->siglock);
> >> +	for_each_thread(p, t)
> >> +		WRITE_ONCE(t->membarrier_sync_core, 1);
> >> +	spin_unlock(&p->sighand->siglock);
> >> +	/*
> >> +	 * Ensure all future scheduler execution will observe the new
> >> +	 * membarrier_sync_core state for this process.
> >> +	 */
> >> +	synchronize_sched();
> >> +}
> >> +
> >>  /**
> >>   * sys_membarrier - issue memory barriers on a set of threads
> >>   * @cmd:   Takes command values defined in enum membarrier_cmd.
> >> @@ -146,6 +174,9 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
> >>  	case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
> >>  		membarrier_private_expedited();
> >>  		return 0;
> >> +	case MEMBARRIER_CMD_REGISTER_SYNC_CORE:
> >> +		membarrier_register_sync_core();
> >> +		return 0;
> >>  	default:
> >>  		return -EINVAL;
> >>  	}
> >> --
> >> 2.11.0
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>